Aristotle is a towering figure in ancient Greek philosophy, who made important contributions to lớn logic, criticism, rhetoric, physics, biology, psychology, mathematics, metaphysics, ethics, và politics. He was a student of Plato for twenty years but is famous for rejecting Plato’s theory of forms. He was more empirically minded than both Plato and Plato’s teacher, Socrates.

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A prolific writer, lecturer, and polymath, Aristotle radically transformed most of the topics he investigated. In his lifetime, he wrote dialogues & as many as 200 treatises, of which only 31 survive. These works are in the size of lecture notes và draft manuscripts never intended for general readership. Nevertheless, they are the earliest complete philosophical treatises we still possess.

As the father of western logic, Aristotle was the first lớn develop a formal system for reasoning. He observed that the deductive validity of any argument can be determined by its structure rather than its content, for example, in the syllogism: All men are mortal; Socrates is a man; therefore, Socrates is mortal. Even if the content of the argument were changed from being about Socrates lớn being about someone else, because of its structure, as long as the premises are true, then the conclusion must also be true. Aristotelian ngắn gọn xúc tích dominated until the rise of modern propositional logic and predicate logic 2000 years later.

The emphasis on good reasoning serves as the backdrop for Aristotle’s other investigations. In his natural philosophy, Aristotle combines logic with observation khổng lồ make general, causal claims. For example, in his biology, Aristotle uses the concept of species to make empirical claims about the functions & behavior of individual animals. However, as revealed in his psychological works, Aristotle is no reductive materialist. Instead, he thinks of the body as the matter, & the psyche as the size of each living animal.

Though his natural scientific work is firmly based on observation, Aristotle also recognizes the possibility of knowledge that is not empirical. In his metaphysics, he claims that there must be a separate & unchanging being that is the source of all other beings. In his ethics, he holds that it is only by becoming excellent that one could achieve eudaimonia, a sort of happiness or blessedness that constitutes the best kind of human life.

Aristotle was the founder of the Lyceum, a school based in Athens, Greece; & he was the first of the Peripatetics, his followers from the Lyceum. Aristotle’s works, exerted tremendous influence on ancient and medieval thought và continue khổng lồ inspire philosophers khổng lồ this day.

Table of Contents

Analytics or “Logic”Theoretical PhilosophyNatural PhilosophyPractical PhilosophyAbbreviationsReferences và Further ReadingSecondary Sources

1. Life and Lost Works

Though our main ancient source on Aristotle’s life, Diogenes Laertius, is of questionable reliability, the outlines of his biography are credible. Diogenes reports that Aristotle’s Greek father, Nicomachus, served as private physician to lớn the Macedonian king Amyntas (DL 5.1.1). At the age of seventeen, Aristotle migrated to Athens where he joined the Academy, studying under Plato for twenty years (DL 5.1.9). During this period Aristotle acquired his encyclopedic knowledge of the philosophical tradition, which he draws on extensively in his works.

Aristotle left Athens around the time Plato died, in 348 or 347 B.C.E. One explanation is that as a resident alien, Aristotle was excluded from leadership of the Academy in favor of Plato’s nephew, the Athenian citizen Speusippus. Another possibility is that Aristotle was forced khổng lồ flee as Philip of Macedon’s expanding power nguồn led khổng lồ the spread of anti-Macedonian sentiment in Athens (Chroust 1967). Whatever the cause, Aristotle subsequently moved to lớn Atarneus, which was ruled by another former student at the Academy, Hermias. During his three years there, Aristotle married Pythias, the niece or adopted daughter of Hermias, và perhaps engaged in negotiations or espionage on behalf of the Macedonians (Chroust 1972). Whatever the case, the couple relocated lớn Macedonia, where Aristotle was employed by Philip, serving as tutor to his son, Alexander the Great (DL 5.1.3–4). Aristotle’s philosophical career was thus directly entangled with the rise of a major power.

After some time in Macedonia, Aristotle returned to Athens, where he founded his own school in rented buildings in the Lyceum. It was presumably during this period that he authored most of his surviving texts, which have the appearance of lecture transcripts edited so they could be read aloud in Aristotle’s absence. Indeed, this must have been necessary, since after his school had been in operation for thirteen years, he again departed from Athens, possibly because a charge of impiety was brought against him (DL 5.1.5). He died at age 63 in Chalcis (DL 5.1.10).

Diogenes tells us that Aristotle was a thin man who dressed flashily, wearing a fashionable hairstyle và a number of rings. If the will quoted by Diogenes (5.1.11–16) is authentic, Aristotle must have possessed significant personal wealth, since it promises a furnished house in Stagira, three female slaves, and a talent of silver khổng lồ his concubine, Herpyllis. Aristotle fathered a daughter with Pythias and, with Herpyllis, a son, Nicomachus (named after his grandfather), who may have edited Aristotle’s Nicomachean Ethics. Unfortunately, since there are few extant sources on Aristotle’s life, one’s judgment about the accuracy and completeness of these details depends largely on how much one trusts Diogenes’ testimony.

Since commentaries on Aristotle’s work have been produced for around two thousand years, it is not immediately obvious which sources are reliable guides khổng lồ his thought. Aristotle’s works have a condensed style & make use of a peculiar vocabulary. Though he wrote an introduction to philosophy, a critique of Plato’s theory of forms, & several philosophical dialogues, these works survive only in fragments. The extant Corpus Aristotelicum consists of Aristotle’s recorded lectures, which cover almost all the major areas of philosophy. Before the invention of the printing press, handwritten copies of these works circulated in the Near East, northern Africa, and southern Europe for centuries. The surviving manuscripts were collected & edited in August Immanuel Bekker’s authoritative 1831–1836 Berlin edition of the Corpus (“Bekker” 1910). All references khổng lồ Aristotle’s works in this article follow the standard Bekker numbering.

The extant fragments of Aristotle’s lost works, which modern commentators sometimes use as the basis for conjectures about his philosophical development, are noteworthy. A fragment of his Protrepticus preserves a striking analogy according khổng lồ which the psyche or soul’s attachment to lớn the body toàn thân is a form of punishment:

The ancients blessedly say that the psyche pays penalty & that our life is for the atonement of great sins. And the yoking of the psyche khổng lồ the body seems very much lượt thích this. For they say that, as Etruscans torture captives by chaining the dead face lớn face with the living, fitting each to lớn each part, so the psyche seems to lớn be stretched throughout, and constrained to all the sensitive members of the body. (Pistelli 1888, 47.24–48.1)

According khổng lồ this allegedly inspired theory, the fetters that bind the psyche lớn the body are similar to lớn those by which the Etruscans torture their prisoners. Just as the Etruscans chain prisoners face lớn face with a dead body toàn thân so that each part of the living body toàn thân touches a part of the corpse, the psyche is said lớn be aligned with the parts of one’s living body. On this view, the psyche is embodied as a painful but corrective atonement for its badness. (See Bos 2003 và Hutchinson & Johnson’s webpage).

The incompatibility of this passage with Aristotle’s view that the psyche is inseparable from the body (discussed below) has been explained in various ways. Neo-Platonic commentators distinguish between Aristotle’s esoteric và exoteric writings, that is, writings intended for circulation within his school, và writings lượt thích the Protrepticus intended for a broader reading public (Gerson 2005, 47–75). Some modern scholars have argued lớn the contrary that the imprisonment of the psyche in the body toàn thân indicates that Aristotle was still a Platonist at the time he composed the Protrepticus, which must have been written earlier than his mature works (Jaeger 1948, 100). Aristotle’s dialogue Eudemus, which contains arguments for the immortality of the psyche, and his Politicus, which is about the ideal statesman, seem to corroborate the view that Aristotle’s exoteric works hold much that is Platonic in spirit (Chroust 1965; 1966). The latter contains the seemingly Platonic assertion that “the good is the most exact of measures” (Kroll 1902, 168: 927b4–5).

But not all agree. Owen (1968, 162–163) argues that Aristotle’s fundamental logical distinction between individual và species depends on an antecedent break with Plato. According khổng lồ this view, Aristotle’s On Ideas (Fine 1993), a collection of arguments against Platonic forms, shows that Aristotle rejected Platonism early in his career, though he later became more sympathetic khổng lồ the master’s views. However, as Lachterman (1980) points out, such historical theses depend on substantive hermeneutical assumptions about how to lớn read Aristotle và on theoretical assumptions about what constitutes a philosophical system. This article focuses not on this historical debate but on the theories propounded in Aristotle’s extant works.

2. Analytics or “Logic”

Aristotle is usually identified as the founder of ngắn gọn xúc tích in the West (although autonomous logical traditions also developed in India và China), where his “Organon,” consisting of his works the Categories, On Interpretation, Prior Analytics, Posterior Analytics, Sophistical Refutations, & Topics, long served as the traditional manuals of logic. Two other works—Rhetoric and Poetics—are not about logic, but also concern how to lớn communicate lớn an audience. Curiously, Aristotle never used the words “logic” or “organon” to lớn refer khổng lồ his own work but calls this discipline “analytics.” Though Aristotelian ngắn gọn xúc tích is sometimes referred lớn as an “art” (Ross 1940, iii), it is clearly not an art in Aristotle’s sense, which would require it khổng lồ be productive of some over outside itself. Nevertheless, this article follows the convention of referring khổng lồ the content of Aristotle’s analytics as “logic.”

a. The Meaning and Purpose of Logic

What is logic for Aristotle? On Interpretation begins with a discussion of meaning, according to lớn which written words are symbols of spoken words, while spoken words are symbols of thoughts (Int.16a3–8). This theory of signification can be understood as a semantics that explains how different alphabets can signify the same spoken language, while different languages can signify the same thoughts. Moreover, this theory connects the meaning of symbols to logical consequence, since commitment to lớn some set of utterances rationally requires commitment khổng lồ the thoughts signified by those utterances & to what is entailed by them. Hence, though Cook Wilson (1926, 30–33) correctly notes that Aristotle nowhere defines logic, it may be called the science of thinking, where the role of the science is not to describe ordinary human reasoning but rather to demonstrate what one ought to lớn think given one’s other commitments. Though the elements of Aristotelian lô ghích are implicit in our conscious reasoning, Aristotelian “analysis” makes explicit what was formerly implicit (Cook Wilson 1926, 49).

Aristotle shows how lô ghích can demonstrate what one should think, given one’s commitments, by developing the syntactical concepts of truth, predication, and definition. In order for a written sentence, utterance, or thought to lớn be true or false, Aristotle says, it must include at least two terms: a subject and a predicate. Thus, a simple thought or utterance such as “horse” is neither true nor false but must be combined with another term, say, “fast” in order to size a compound—“the horse is fast”—that describes reality truly or falsely. The written sentence “the horse is fast” has meaning insofar as it signifies the spoken sentence, which in turn has meaning in virtue of its signifying the thought that the horse is fast (Int.16a10–18, Cat.13b10–12, DA 430a26–b1). Aristotle holds that there are two kinds of constituents of meaningful sentences: nouns & their derivatives, which are conventional symbols without tense or aspect; & verbs, which have a tense and aspect. Though all meaningful speech consists of combinations of these constituents, Aristotle limits xúc tích to the consideration of statements, which assert or deny the presence of something in the past, present, or future (Int.17a20–24).

Aristotle analyzes statements as cases of predication, in which a predicate phường is attributed to lớn a subject S as in a sentence of the size “S is P.” Since he holds that every statement expresses something about being, statements of this khung are lớn be read as “S is (exists) as a P” (Bäck 2000, 11). In every true predication, either the subject và predicate are of the same category, or the subject term refers khổng lồ a substance while the predicate term refers lớn one of the other categories. The primary substances are individuals, while secondary substances are species and genera composed of individuals (Cat.2a11–18). This distinction between primary và secondary reflects a dependence relation: if all the individuals of a species or genus were annihilated, the species and genus could not, in the present tense, be truly predicated of any subject.

Every individual is of a species và that species is predicated of the individual. Every species is the member of a genus, which is predicated of the species & of each individual of that species (Cat.2b13–22). For example, if Callias is of the species “man,” & the species is a thành viên of the genus “animal,” then “man” is predicated of Callias, and “animal” is predicated both of “man” và of Callias. The individual, Callias, inherits the predicate “animal” in virtue of being of the species “man.” But inheritance stops at the individual and does not apply khổng lồ its proper parts. For example, “man” is not truly predicated of Callias’ hand. A genus can be divided with reference lớn the specific differences among its members; for example, “biped” differentiates “man” from “horse.”

While no definition can be given of an individual or primary substance such as Callias, when one gives the genus and all the specific differences possessed by a kind of thing, one can define a thing’s species. A specific difference is a predicate that falls under one of the categories. Thus, Aristotelian categories can be seen as a taxonomical scheme, a way of organizing predicates for discovery, or as a metaphysical doctrine about the kinds of beings there are. But any reading must accommodate Aristotle’s views that primary substances are never predicated of a subject (Cat.3a6), that a predicate may fall under multiple categories (Cat.11a20–39), và that some terms, such as “good,” are predicated in all the categories (NE 1096a23–29). Moreover, definitions are reached not by demonstration but by other kinds of inquiry, such as dialectic, the art by which one makes divisions in a genus; & induction, which can reveal specific differences from the observation of individual examples.

b. Demonstrative Syllogistic

Syllogistic reasoning builds on Aristotle’s theory of predication, showing how to lớn reason from premises to conclusions. A syllogism is a discourse in which when taking some statements as premises a different statement can be shown to follow as a conclusion (AnPr.24b18–22). The basic form of the Aristotelian syllogism involves a major premise, a minor premise, và a conclusion, so that it has the form

If A is predicated of all B,

And B is predicated of all C,

Then A is predicated of all C.

This is an assertion of formal logic, since by removing the values of the variables A, B, & C, one treats the inference formally, such that the values of the subject A và predicates B and C are not given as part of the syllogistic form (Łukasiewicz, 10–14).

Though this khung can be utilized in dialectic, in which the major term A is related khổng lồ C through the middle term B credibly rather than necessarily (AnPo.81b10–23), Aristotle is mainly concerned with how lớn use syllogistic in what he calls demonstrative reasoning, that is, in inference from certain premises khổng lồ a certain conclusion. A demonstrative syllogism is not concerned with a mere opinion but proves a cause, that is, answers a “why” question (AnPo.85b 23–26).

The validity of a syllogism can be tested through comparison of four basic types of assertions: All S are phường (A), No S are p (E), Some S are p. (I), và Some S are not p. (O). The truth conditions of these assertions are determined relationally: through contradiction, in which if one of the assertions is true, the other must be false; contrariety, in which both assertions cannot be true; & subalternation, in which the universal assertion’s being true requires that the particular assertion must be true, as well. These relationships are summed up in the traditional square of opposition used by medieval Aristotelian logicians. (see Groarke, Aristotle: Logic).


Figure 1: The Traditional Square of Opposition illustrates the relations between the fundamental judgment-forms in Aristotelian syllogistic: (A) All S are P, (E) No S are P, (I) Some S are P, và (O) Some S are not P.

Syllogistic may be employed dialectically when the premises are accepted on the authority of common opinion, from tradition, or from the wise. In any dialectical syllogism, the premises can be generally accepted opinions rather than necessary principles (Top.100a25–b21). At least some premises in rhetorical proofs must be not necessary but only probable, happening only for the most part.

When the premises are known, and conclusions are shown to lớn follow from those premises, one gains knowledge by demonstration. Demonstration is necessary (AnPo.73a21–27) because the conclusion of a demonstrative syllogism predicates something that is either necessarily true or necessarily false of the subject of the premise. One has demonstrative knowledge when one knows the premises và has derived a necessary conclusion from them, since the cause given in the premises explains why the conclusion is so (AnPo.75a12–17, 35–37). Consequently, valid demonstration depends on the known premises containing terms for the genus of which the species in the conclusion is a member (AnPo.76a29–30).

One interesting problem that arises within Aristotle’s theory of demonstration concerns the connection between temporality and necessity. By the principle of excluded middle, necessarily, either there will be a sea-battle tomorrow or there will not be a sea-battle tomorrow. But since the sea-battle itself has yet neither come about nor failed lớn come about, it seems that one must say, paradoxically, that one alternative is necessary but that either alternative might come about (Int.19a22–34). The question of how to trương mục for unrealized possibilities and necessities is part of Aristotle’s modal syllogistic, which is discussed at length in his Prior Analytics. For a discussion, see Malink (2013).

c. Induction, Experience, and Principles

Whenever a speaker reasons from premises, an auditor can ask for their demonstration. The speaker then needs to lớn adduce additional premises for that demonstration. But if this line of questioning went on interminably, no demonstration could be made, since every premise would require a further demonstration, ad infinitum. In order khổng lồ stop an infinite regress of premises, Aristotle postulates that for an inference khổng lồ count as demonstrative, one must know its indemonstrable premises (AnPo.73a16–20). Thus, demonstrative science depends on the view that all teaching and learning proceed from already present knowledge (AnPo.72b5–20). In other words, the possibility of making a complete argument, whether inductive or deductive, depends on the reasoner possessing the concept in question.

The acquisition of concepts must in some way be perceptual, since Aristotle says that universals come khổng lồ rest in the soul through experience, which comes about from many memories of the same thing, which in turn comes about by perception (AnPo.99b32–100a9). However, Aristotle holds that some concepts are already manifested in one’s perceptual experience: children initially điện thoại tư vấn all men father and all women mother, only later developing the capacity to apply the relevant concepts to particular individuals (Phys.184b3–5). As Cook Wilson (1926, 45) puts it, perception is in a way already of a universal. Upon learning khổng lồ speak, the child already possesses the concept “mother” but does not grasp the conditions of its correct application. The role of perception, và hence of memory and experience, is then not lớn supply the child with universal concepts but to fix the conditions under which they are correctly predicated of an individual or species. Hence the ability lớn arrive at definitions, which serve as starting points of a science, rests on the human being’s natural capacity to lớn use language and on the culturally specific social & political conditions in which that capacity is manifested (Winslow 2013, 45–49).

While deduction proceeds by a size of syllogistic reasoning in which the major & minor premise both predicate what is necessarily true of a subject, inductive reasoning moves from particulars to lớn universals, so it is impossible lớn gain knowledge of universals except by induction (AnPo.81a38–b9). This movement, from the observation of the same occurrence, to an experience that emerges from many memories, to a universal judgment, is a cognitive process by which human beings understand reality (see AnPo.88a2–5, Met.980b28–981a1, EN 1098b2–4, 1142a12).

But what makes such an inference a good one? Aristotle seems to say an inductive inference is sound when what is true in each case is also true of the class under which the cases fall (AnPr.68b15–29). For example, it is inferred from the observation that each kind of bileless animal (men, horses, mules, & so on) is long-lived just when the following syllogism is sound: (1) All men, horses, mules, and so on are long-lived; (2) All long-lived animals are bileless; therefore (3) all men, horses, mules, and so on are bileless (see Groarke sections 10 and 11). However, Aristotle does not think that knowledge of universals is pieced together from knowledge of particulars but rather he thinks that induction is what allows one to actualize knowledge by grasping how the particular case falls under the universal (AnPr.67a31–b5).

A true definition reveals the essential nature of something, what it is to lớn be that thing (AnPo.90b30–31). A sound demonstration shows what is necessary of an observed subject (AnPo.90b38–91a5). It is essential, however, that the observation on which a definition is based be inductively true, that is, that it be based on causes rather than on chance. Regardless of whether one is asking what something is in a definition or why something is the way it is by giving its cause, it is only when the principles or starting points of a science are given that demonstration becomes possible. Since experience is what gives the principles of each science (AnPr.46a17–27), lô ghích can only be employed at a later stage to lớn demonstrate conclusions from these starting points. This is why logic, though it is employed in all branches of philosophy, is not a part of philosophy. Rather, in the Aristotelian tradition, ngắn gọn xúc tích is an instrument for the philosopher, just as a hammer và anvil are instruments for the blacksmith (Ierodiakonou 1998).

d. Rhetoric & Poetics

Just as dialectic searches for truth, Aristotelian rhetoric serves as its counterpart (Rhet.1354a1), searching for the means by which truth can be grasped through language. Thus, rhetorical demonstration, or enthymeme, is a kind of syllogism that strictly speaking belongs to lớn dialectic (Rhet.1355a8–10). Because rhetoric uses the particularly human capacity of reason lớn formulate verbal arguments, it is the art that can cause the most harm when it is used wrongly. It is thus not a technique for persuasion at any cost, as some Sophists have taught, but a fundamentally second-personal way of using language that allows the auditor to reach a judgment (Grimaldi 1972, 3–5). More fundamentally, rhetoric is defined as the detection of persuasive features of each subject matter (Rhet.1355b12–22).

Proofs given in speech depend on three things: the character (ethos) of the speaker, the disposition (pathos) of the audience, & the meaning (logos) of the sounds và gestures used (Rhet.1356a2–6). Rhetorical proofs show that the speaker is worthy of credence, producing an emotional state (pathos) in the audience, or demonstrating a consequence using the words alone. Aristotle holds that ethos is the most important of these elements, since trust in the speaker is required if one is to lớn believe the speech. However, the best speech balances ethos, pathos, and logos. In rhetoric, enthymemes play a deductive role, while examples play an inductive role (Rhet.1356b11–18).

The deductive khung of rhetoric, enthymeme, is a dialectical syllogism in which the probable premise is suppressed so that one reasons directly from the necessary premise khổng lồ the conclusion. For example, one may reason that an animal has given birth because she has milk (Rhet.1357b14–16) without providing the intermediate premise. Aristotle also calls this deductive size of inference “reasoning by signs” or “reasoning from evidence,” since the animal’s having milk is a sign of, or evidence for, her having given birth. Though the audience seemingly “immediately” grasps the fact of birth without it being given in perception, the passage from the perception lớn the fact is inferential & depends on the background assumption of the suppressed premise.

The inductive khung of rhetoric, reasoning from example, can be illustrated as follows. Peisistratus in Athens & Theagenes in Megara both petitioned for guards shortly before establishing themselves as tyrants. Thus, someone plotting a tyranny requests a guard (Rhet.1357b30–37). This proof by example does not have the force of necessity or universality and does not count as a case of scientific induction, since it is possible someone could petition for a guard without plotting a tyranny. But when it is necessary khổng lồ base some decision, for example, whether to grant a request for a bodyguard, on its likely outcome, one must look lớn prior examples. It is the work of the rhetorician to lớn know these examples and to formulate them in such a way as khổng lồ suggest definite policies on the basis of that knowledge.

Rhetoric is divided into deliberative, forensic, & display rhetoric. Deliberative rhetoric is concerned with the future, namely with what to lớn do, and the deliberative rhetorician is khổng lồ discuss the advantages and harms associated with a specific course of action. Forensic rhetoric, typical of the courtroom, concerns the past, especially what was done and whether it was just or unjust. Display rhetoric concerns the present and is about what is noble or base, that is, what should be praised or denigrated (Rhet.1358b6–16). In all these domains, the rhetorician practices a kind of reasoning that draws on similarities & differences lớn produce a likely prediction that is of value to lớn the political community.

A common characteristic of insightful philosophers, rhetoricians, và poets is the capacity lớn observe similarities in things that are unlike, as Archytas did when he said that a judge & an alter are kindred, since someone who has been wronged has recourse to lớn both (Rhet.1412a10–14). This noticing of similarities và differences is part of what separates those who are living the good life from those who are merely living (Sens.437a2–3). Likewise, the highest achievement of poetry is khổng lồ use good metaphors, since khổng lồ make metaphors well is lớn contemplate what is lượt thích (Poet.1459a6–9). Poetry is thus closely related to both philosophy và rhetoric, though it differs from them in being fundamentally mimetic, imitating reality through an artistic form.

Imitation in poetry is achieved by means of rhythm, language, and harmony (Poet.1447a13–16, 21–22). While other arts chia sẻ some or all these elements—painting imitates visually by the same means, while dance imitates only through rhythm—poetry is a kind of vocalized music, in which voice và discursive meaning are combined. Aristotle is interested primarily in the kinds of poetry that imitate human actions, which fall into the broad categories of comedy và tragedy. Comedy is an imitation of worse types of people and actions, which reflect our lower natures. These imitations are not despicable or painful, but simply ridiculous or distorted, and observing them gives us pleasure (Poet.1449a31–38). Aristotle wrote a book of his Poetics on comedy, but the book did not survive. Hence, through a historical accident, the traditions of aesthetics và criticism that proceed from Aristotle are concerned almost completely with tragedy.

Tragedy imitates actions that are excellent and complete. As opposed lớn comedy, which is episodic, tragedy should have a single plot that ends in a presentation of pity và fear & thus a catharsis—a cleansing or purgation—of the passions (Poet.1449b24–28). (As discussed below, the passions or emotions also play an important role in Aristotle’s practical philosophy.) The most important aspect of a tragedy is how it uses a story or myth lớn lead the psyches of its audience to lớn this catharsis (Poet.1450a32–34). Since the beauty or fineness of a thing—say, of an animal—consists in the orderly arrangement of parts of a definite magnitude (Poet.1450b35–38), the parts of a tragedy should also be proportionate.

A tragedy’s ability to lớn lead the psyche depends on its myth turning at a moment of recognition at which the central character moves from a state of ignorance to a state of knowledge. In the best case, this recognition coincides with a reversal of intention, such as in Sophocles’ Oedipus, in which Oedipus recognizes himself as the man who was prophesied to lớn murder his father and marry his mother. This moment produces pity and fear in the audience, fulfilling the purpose of tragic imitation (Poet.1452a23–b1). The pity và fear produced by imitative poetry are the source of a peculiar form of pleasure (Poet.1453b11–14). Though the imitation itself is a kind of technique or art, this pleasure is natural to lớn human beings. Because of this potential lớn produce emotions và lead the psyche, poetics borders both on what is well natured & on madness (Poet.1455a30–34).

Why bởi vì people write plays, read stories, and watch movies? Aristotle thinks that because a series of sounds with minute differences can be strung together to form conventional symbols that name particular things, hearing has the accidental property of supporting meaningful speech, which is the cause of learning (Sens.437a10–18). Consequently, though sound is not intrinsically meaningful, voice can carry meaning when it “ensouled,” transmitting an appearance about how absent things might be (DA 420b5-10, 27–33). Poetry picks up on this natural capacity, artfully imitating reality in language without requiring that things are actually the way they are presented as being (Poet.1447a13–16).

The poet’s consequent power lớn lead the psyche through true or false imitations, lượt thích the rhetorician’s power lớn lead it through persuasive speech, leads to lớn a parallel question: how should the poet use his power? Should the poet imitate things as they are, or as they should be? Though it is clear that the standard of correctness in poetry và politics is not the same (Poet.1460b13–1461a1), the question of how và to what extent the state should constrain poetic production remains unresolved.

3. Theoretical Philosophy

Aristotle’s classification of the sciences makes a distinction between theoretical philosophy, which aims at contemplation, và practical philosophy, which aims at action or production. Within theoretical philosophy, first philosophy studies objects that are motionless và separate from material things, mathematics studies objects that are motionless but not separate, và natural philosophy studies objects that are in motion và not separate (Met.1026a6–22).

This threefold distinction among the beings that can be contemplated corresponds to lớn the cấp độ of precision that can be attained by each branch of theoretical philosophy. First philosophy can be perfectly exact because there is no variation among its objects and thus it has the potential to give one knowledge in the most profound sense. Mathematics is also absolutely certain because its objects are unchanging, but since there are many mathematical objects of a given kind (for example, one could draw a potentially infinite number of different triangles), mathematical proofs require a peculiar method that Aristotle calls “abstraction.” Natural philosophy gives less exact knowledge because of the diversity and variability of natural things & thus requires attention khổng lồ particular, empirical facts. Studies of nature—including treatises on special sciences lượt thích cosmology, biology, & psychology—account for a large part of Aristotle’s surviving writings.

a. Natural Philosophy

Aristotle’s natural philosophy aims for theoretical knowledge about things that are subject lớn change. Whereas all generated things, including artifacts & products of chance, have a source that generates them, natural change is caused by a thing’s inner principle và cause, which may accordingly be called the thing’s “nature” (Phys.192b8–20). To grasp the nature of a thing is khổng lồ be able to lớn explain why it was generated essentially: the nature of a thing does not merely contribute lớn a change but is the primary determinant of the change as such (Waterlow 1982, p.28).

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Though some hold that Aristotle’s principles are epistemic, explanatory concepts, principles are best understood ontologically as unique, continuous natures that govern the generation & self-preservation of natural beings. Lớn understand a thing’s nature is primarily to lớn grasp “how a being displays itself by its nature.” Such a grasp counts as a correct explanation only insofar as it constitutes a size of understanding of beings in themselves as they give themselves (Winslow 2007, 3–7).

Aristotle’s mô tả tìm kiếm of principles as the start & end of change (Phys.235b6) distinguishes between two kinds of natural change. Substantial change occurs when a substance is generated (Phys.225a1–5), for example, when the seed of a plant gives rise khổng lồ another plant of the same kind. Non-substantial change occurs when a substance’s accidental qualities are affected, for example, the change of color in a ripening pomegranate. Aristotelians describe this as the activity of contraries of blackness & whiteness in the plant’s material in which the fruit of the pomegranate, as its juices become colored by ripening, itself becomes shaded, changing khổng lồ a purple color (de Coloribus 796a20–26). Ripening occurs when heat burns up the air in the part of the plant near the ground, causing convection that alters the originally light màu sắc of the fruit to its dark contrary (de Plantis 820b19–23). Both kinds of change are caused by the plant’s containing in itself a principle of change. In substantial change, a new primary substance is generated; in non-substantial change, some property of preexisting substance changes to lớn a contrary state.

A process of change is completely described when its four causes are given. This can be illustrated with Aristotle’s favorite example of the production of a bronze sculpture. The (1) material cause of the change is given when the underlying matter of the thing has been described, such as the bronze matter of which a statue is composed. The (2) formal cause is given when one says what kind of thing the thing is, for example, “sphere” for a bronze sphere or “Callias” for a bronze statue of Callias. The (3) efficient cause is given when one says what brought the change about, for example, when one names the sculptor. The (4) final cause is given when one says the purpose of the change, for example, when one says why the sculptor chose to lớn make the bronze sphere (Phys.194b16–195a2).

In natural change the principle of change is internal, so the formal, efficient, và final causes typically coincide. Moreover, in such cases, the metaphysical & epistemological sides of causal explanation are normally unified: a formal cause counts both as a thing’s essence—what it is khổng lồ be that thing—and as its rational trương mục or reason for being (Bianchi 2014, 35). Thus, when speaking of natural changes rather than the making of an artifact, Aristotle will usually offer “hylomorphic” descriptions of the natural being as a compound of matter và form.

Because Aristotle holds that a thing’s underlying nature is analogous to lớn the bronze in a statue (Phys.191a7–12), some have argued that the underlying thing refers to lớn “prime matter,” that is, to an absolutely indeterminate matter that has no form. But Cook (1989) has shown that the underlying thing normally means matter that already has some form. Indeed, Aristotle claims that the matter of perceptible things has no separate existence but is always already informed by a contrary (Gen et Corr.329a25–27). The matter that traditional natural philosophy calls the “elements”—fire, water, air, and earth—already has the khung of the basic contraries, hot and cold, & moist & dry, so that, for example, fire is matter with a hot and dry size (Gen et Corr.330a25–b4). Thus, even in the most basic cases, matter is always actually informed, even though the size is potentially subject lớn change. For example, throwing water on a fire cools & moistens it, & bringing about a new unique in the underlying material. Thus, Aristotle sometimes describes natural powers as being latent or active “in the material” (Meteor.370b14–18).

Aristotle’s general works in natural philosophy offer analyses of concepts necessarily assumed in accounts of natural processes, including time, change, và place. In general, Aristotle will describe changes that occur in time as arising from a potential, which is actualized when the change is complete. However, what is actual is logically prior to what is potential, since a potentiality aims at its own actualization and thus must be defined in terms of what is actual. Indeed, generically the actual is also temporally prior lớn potentiality, since there must invariably be a preexisting actuality that brings the potentiality lớn its own actualization (Met.1049b4–19). Perhaps because of the priority of the actual to the potential, whenever Aristotle speaks of natural change, he is concerned with a field of naturalistic inquiry that is continuous rather than atomistic & purposeful or teleological rather than mechanical. In his more specific naturalistic works, Aristotle lays out a program of specialized studies about the heavens & Earth, living things, and the psyche.

i. Cosmology and Geology

Aristotle’s cosmology depends on the basic observation that while bodies on Earth either rise khổng lồ a limit or fall khổng lồ Earth, heavenly bodies keep moving, without any apparent external force being exerted on them (DC 284a10–15). On the basis of this observation, he distinguishes between circular motion, which is operative in the “superlunary” heavens, & rectilinear motion on “sublunary” Earth below the Moon. Since all sublunary bodies move in a rectilinear pattern, the heavenly bodies must be composed of a different body toàn thân that naturally moves in a circle (DC 269a2–10, Meteor.340b6–15). This body toàn thân cannot have an opposite, because there is no opposite to circular motion (DC 270a20, compare 269a19–22). Indeed, since there is nothing khổng lồ oppose its motion, Aristotle supposes that this fifth element, which he calls “aether,” as well as the heavenly bodies composed of it, move eternally (DC 275b1–5, 21–25).

In Aristotle’s view the heavens are ungenerated, neither coming to be nor passing away (DC 279b18–21, 282a24–30). Aristotle defines time as the number of motion, since motion is necessarily measured by time (Phys.224a24). Thus, the motion of the eternal bodies is what makes time, so the life & being of sublunary things depends on them. Indeed, Aristotle says that their own time is eternal or “aeon.”

Noticing that water naturally forms spherical droplets và that it flows towards the lowest point on a plane, Aristotle concludes that both the heavens và the earth are spherical (DC 287b1–14). This is further confirmed by observations of eclipses (DC 297b23–31) and that different stars are visible at different latitudes (DC 297b14–298a22).

The gathering of such observations is an important part of Aristotle’s scientific procedure (AnPr.46a17–22) & sets his theories above those of the ancients that lacked such “experience” (Phys.191a24–27). Just as in his biology, where Aristotle draws on animal anatomy observed at sacrifices (HA 496b25) và records reports from India (HA 501a25), so in his astronomy he cites Egyptian và Babylonian observations of the planets (DC 292a4–9). By gathering evidence from many sources, Aristotle is able to lớn conclude that the stars and the Moon are spherical (DC 291b11–20) and that the Milky Way is an appearance produced by the sight of many stars moving in the outermost sphere (Meteor.346a16–24).

Assuming the hypothesis that the Earth does not move (DC 289b6–7), Aristotle argues that there are in the heavens both stars, which are large và distant from earth, và planets, which are smaller và closer. The two can be distinguished since stars appear to lớn twinkle while planets vày not (Aristotle somewhat mysteriously attributes the twinkling stars to their distance from the eye of the observer) (DC 290b14–24). Unlike earthly creatures, which move because of their distinct organs or parts, both the moving stars and the unmoving heaven that contains them are spherical (DC 289a30–b11). As opposed to lớn superlunary (eternal) substances, sublunary beings, like clouds & human beings, participate in the eternal through coming to be and passing away. In doing so, the individual or primary substance is not preserved, but rather the species or secondary substance is preserved (as we shall see below, the same thought is utilized in Aristotle’s explanation of biological reproduction) (Gen et Corr.338b6–20).

Aristotle holds that the Earth is composed of four spheres, each of which is dominated by one of the four elements. The innermost & heaviest sphere is predominantly earth, on which rests upper spheres of water, air, and fire. The sun acts to lớn burn up or vaporize the water, which rises khổng lồ the upper spheres when heated, but when cooled later condenses into rain (Meteor.354b24–34). If unqualified necessity is restricted lớn the superlunary sphere, teleology—the seeking of ends that may or may not be brought about—seems to be limited khổng lồ the sublunary sphere.

Due to his belief that the Earth is eternal, being neither created nor destroyed, Aristotle holds that the epochs move cyclically in patterns of increase & decrease (Meteor.351b5–19). Aristotle’s cyclical understanding of both natural and human history is implicit in his comment that while Egypt used to be a fertile land, it has over the centuries grown arid (Meteor.351b28–35). Indeed, parts of the world that are ocean periodically become land, while those that are land are covered over by ocean (Meteor.253a15–24). Because of periodic catastrophes, all human wisdom that is now sought concerning both the arts & divine things was previously possessed by forgotten ancestors. However, some of this wisdom is preserved in myths, which pass on knowledge of the divine by allegorically portraying the gods in human or animal form so that the masses can be persuaded khổng lồ follow laws (Met.1074a38-b14, compare Meteor.339b28–30, Pol.1329b25).

Aristotle’s geology or earth science, given in the latter books of his Meteorology, offers theories of the formation of oceans, of wind and rainfall, & of other natural events such as earthquakes, lightning, và thunder. His theory of the rainbow suggests that drops of water suspended in the air size mirrors which reflect the multiply-colored visual ray that proceeds from the eye without its proper magnitude (Meteor.373a32–373b34). Though the explanations given by Aristotle of these phenomena contradict those of modern physics, his careful observations often give interest khổng lồ his account.

Aristotle’s material science offers the first description of what are now called non-Newtonian fluids—honey & must—which he characterizes as liquids in which earth and heat predominate (Meteor.385b1–5). Although the Ancient Greeks did not distill alcohol, he reports on the accidental distillation of some ethanol from wine (“sweet wine”), which he observes is more combustible than ordinary wine (Meteor.387b10–14). Finally, Aristotle’s material science makes an informative distinction between compounds, in which the constituents maintain their identity, and mixtures, in which one constituent comes khổng lồ dominate or in which a new kind of material is generated (see Sharvy 1983 for discussion). Though it would be inaccurate to lớn describe him as a methodological empiricist, Aristotle’s collection & careful recording of observations shows that in all of his scientific endeavors, his explanations were designed to accord with publicly observable natural phenomena.

ii. Biology

The phenomenon of life, as opposed khổng lồ inanimate nature, involves distinctive types of change (Phys.244b10–245a5) and thus requires distinctive types of explanation. Biological explanations should give all four causes of an organism or species—the material of which it is composed, the processes that bring it about, the particular form it has, & its purpose. For Aristotle, the investigation of individual organisms gives one causal knowledge since the individuals belong lớn a natural kind. Men & horses both have eyes, which serve similar functions in each of them, but because their species are different, a man’s eye is similar to lớn the eyes of other men, while a horse’s eyes are similar to lớn the eyes of other horses (HA 486a15–20). Biology should explain both why homologous forms exist in different species and the ways in which they differ, and therefore the causes for the persistence of each natural kind of living thing.

Although all four causes are relevant in biology, Aristotle tends to group final causes with formal causes in teleological explanations, & material causes with efficient causes in mechanical explanations. Boylan (section 4) shows, for example, that Aristotle’s teleological explanation of respiration is that it exists in order khổng lồ bring air into the toàn thân to produce pneuma, which is the means by which an animal moves itself. Aristotle’s mechanical explanation is that air that has been heated in the lungs is pushed out by colder air outside the body (On Breath 481b10–16, PA 642a31–b4).

Teleological explanations are necessary conditionally; that is, they depend on the assumption that the biologist has correctly identified the kết thúc for the sake of which the organism behaves as it does. Mechanical explanations, in distinction, have absolute necessity in the sense that they require no assumptions about the purpose of the organism or behavior. In general, however, teleological explanations are more important in biology (PA 639b24–26), because making a distinction between living and inanimate things depends on the assumption that “nature does nothing in vain” (GA 741b5).

The final cause of each kind corresponds khổng lồ the reason that it continues to persist. As opposed khổng lồ superlunary, eternal substances, sublunary living things cannot preserve themselves individually or, as Aristotle puts it, “in number.” Nevertheless, because living is better than not living (EN 1170b2–5), each individual has a natural drive lớn preserve itself “in kind.” Such a drive for self-preservation is the primary way in which living creatures participate in the divine (DA 415a25–b7). Nutrition and reproduction therefore are, in Aristotle’s philosophy, value-laden and goal-directed activities. They are activated, whether consciously or not, for the good of the species, namely for its continuation, in which it imitates the eternal things (Gen et Corr.338b12–17). In this way, life can be considered lớn be directed toward & imitative of the divine (DC 292b18–22).

This basic teleological or goal-directed orientation of Aristotle’s biology allows him to lớn explain the various functions of living creatures in terms of their growth và preservation of form. Perhaps foremost among these is reproduction, which establishes the continuity of a species through a generation. As Aristotle puts it, the seed is temporally prior to lớn the fully developed organism, since each organism develops from a seed. But the fully developed organism is logically prior to the seed, since it is the end or final cause, for the sake of which the seed is produced (PA 641b29–642a2).

In asexual reproduction in plants và animals, the seed is produced by an individual organism và implanted in soil, which activates it & thus actualizes its potentiality lớn become an organism of the kind from which it was produced. Aristotle thus utilizes a conception of “type” as an endogenous teleonomic principle, which explains why an individual animal can produce other animals of its own type (Mayr 1982, 88). Hence, the natural kind lớn which an individual belongs makes it what it is. Animals of the same natural kind have the same size of life và can reproduce with one another but not with animals of other kinds.

In animal sexual reproduction, Aristotle understands the seed possessed by the male as the source or principle of generation, which contains the form of the animal & must be implanted in the female, who provides the matter (GA 716a14–25). In providing the form, the male sets up the formation of the embryo in the matter provided by the female, as rennet causes milk to coagulate into cheese (GA 729a10–14). Just as rennet causes milk lớn separate into a solid, earthy part (or cheese), & a fluid, watery part (or whey), so the semen causes the menstrual fluid to set. In this process, the principle of growth potentially contained in the seed is activated, which, lượt thích a seed planted in soil, produces an animal’s body as the embryo (GA 739b21–740a9).

The size of the animal, its psyche, may thus be said to lớn be potentially in the matter, since the matter contains all the necessary nutrients for the production of the complete organism. However, it is invariably the male that brings about the reproduction by providing the principle of the perceptual soul, a process Aristotle compares with the movement of automatic puppets by a mover that is not in the puppet (GA 741b6–15). (Whether the female produces the nutritive psyche is an mở cửa question.) Thus, form or psyche is provided by the male, while the matter is provided by the female: when the two come together, they size a hylomorphic product—the living animal.

While the khung of an animal is preserved in kind by reproduction, organisms are also preserved individually over their natural lifespans through feeding. In species that have blood, feeding is a kind of concoction, in which food is chewed & broken down in the stomach, then enters the blood, & is finally cooked up to size the external parts of the body. In plants, feeding occurs by the nutritive psyche alone. But in animals, the senses exist for the sake of detecting food, since it is by the senses that animals pursue what is beneficial và avoid what is harmful. In human beings, a similar explanation can be given of the intellectual powers: understanding & practical wisdom exist so that human beings might not only live but also enjoy the good life achievable by kích hoạt (Sens.436b19–437a3).

Although Aristotle’s teleology has been criticized by some modern biologists, others have argued that his biological work is still of interest lớn naturalists. For example, Haldane (1955) shows that Aristotle gave the earliest report of the bee waggle dance, which received a comprehensive explanation only in the 20th century work of Von Frisch. Aristotle also observed lordosis behavior in cattle (HA 572b1–2) và notes that some plants & animals are divisible (Youth and Old Age 468b2–15), a fact that has been vividly illustrated in modern studies of planaria. Even when Aristotle’s biological explanations are incorrect, his observations may be of enduring value.

iii. Psychology

Psychology is the study of the psyche, which is often translated as “soul.” While prior philosophers were interested in the psyche as a part of political inquiry, for Aristotle, the study of the psyche is part of natural science (Ibn Bajjah 1961, 24), continuous with biology. This is because Aristotle conceives of the psyche as the form of a living being, the toàn thân being its material. Although the psyche and toàn thân are never really separated, they can be given different descriptions. For example, the passion of anger can be described physiologically as a boiling of the blood around the heart, while it can be described dialectically as the desire to pay back with pain someone who has insulted one (DA 403a25–b2). While the physiologist examines the material & efficient causes, the dialectician considers only the form & definition of the object of investigation (DA 403a30–b3). Since the psyche is “the first principle of the living thing” (DA 402a6–7), neither the dialectical method nor the physiological method nor a combination of the two is sufficient for a systematic trương mục of the psyche (DA 403a2, b8). Rather than relying on dialectical or materialist speculation, Aristotle holds that demonstration is the proper method of psychology, since the starting point is a definition (DA 402b25–26), & the psyche is the form and definition of a living thing.

Aristotle conceives of psychology as an exact science, with greater precision than the lesser sciences (DA 402a1–5), and accordingly offers a complete sequence of the kinds or “parts” of psyche. The nutritive psyche—possessed by both plants và animals—is responsible for the basic functions of nourishment and reproduction. Perception is possible only in an animal that also has the nutritive nguồn that allows it khổng lồ grow và reproduce, while desire depends on perceiving the object desired, & locomotion depends on desiring objects in different locations (DA 415a1–8). More intellectual powers lượt thích imagination, judgment, and understanding itself exist only in humans, who also have the lower powers.

The succession of psychological powers ensures the completeness, order, và necessity of the relations of psychological parts. Lượt thích rectilinear figures, which proceed from triangles lớn quadrilaterals, to lớn pentagons, & so forth, without there being any intermediate forms, there are no other psyches than those in this succession (DA 414b20–32). This demonstrative approach ensures that although the methods of psychology & physiology are distinct, psychological divisions maps onto biological distinctions. For Aristotle, the parts of the psyche are not separable or “modular” but related genetically: each posterior part of the psyche “contains” the parts before it, and each lower part is the necessary but not sufficient condition for possession of the part that comes after it.

The psyche is defined by Aristotle as the first actuality of a living animal, which is the size of a natural body toàn thân potentially having life (DA 412a19–22). This size is possessed even when it is not being used; for example, a sleeping person has the power khổng lồ hear a melody, though while he is sleeping, he is not exercising the power. In distinction, though a corpse looks just lượt thích a sleeping body, it has no psyche, since it lacks the power to lớn respond to lớn such stimuli. The second actuality of an animal comes when the nguồn is actually exercised such as when one actually hears the melody (DA 417b9–16).

Perception is the reception of the size of an object of perception without its matter, just as wax receives the seal of a ring without its iron or gold (DA 424a17–28). When one sees wine, for example, one perceives something dark & liquid without becoming dark and liquid. Some hold that Aristotle thinks the reception of the size happens in matter so that part of the toàn thân becomes lượt thích the object perceived (for example, one’s eye might be dark while one is looking at wine). Others hold that Aristotelian perception is a spiritual change so that no bodily change is required. But presumably one is changing both bodily và spiritually all the time, even when one is not perceiving. Consequently, the formulation that perception is of “form without matter” is probably not intended lớn describe physiological or spiritual change but rather khổng lồ indicate the conceptual nature of perception. For, as discussed in the section on first philosophy below, Aristotle considers forms to lớn be definitions or concepts; for example, one defines “horse” by articulating its form. If he is using “form” in the same way in his discussion of perception, he means that in perceiving something, such as in seeing a horse, one gains an awareness of it as it is; that is, one grasps the concept of the horse. In that case, all the doctrine means is that perception is conceptual, giving one a grasp not just of parts of perceptible objects, say, the màu sắc and shape of a horse, but of the objects themselves, that is, of the horse as horse. Indeed, Aristotle describes perception as conferring knowledge of particulars and in that sense being like contemplation (DA 417b19–24).

This theory of perception distinguishes three kinds of perceptible objects: proper sensibles, which are perceived only by one sense modality; common sensibles, which are perceived by all the senses; and accidental sensibles, which are facts about the sensible object that are not directly given (DA 418a8–23). For example, in seeing wine, its color is a proper sensible, its volume a common sensible, và the fact that it belongs lớn Callias an accidental sensible. While one normally could not be wrong about the wine’s color, one might overestimate or underestimate its volume under nonstandard conditions, and one is apt to be completely wrong about the accidental sensible (for example, Callias might have sold the wine).

The five senses are distinguished by their proper sensibles: though the wine’s màu sắc might accidentally make one aware that it is sweet, color is proper to lớn sight và sweetness lớn taste. But this raises a question: how vày the different senses work together lớn give one a coherent experience of reality? If they were not coordinated, then one would perceive each chất lượng of an object separately, for example, darkness và sweetness without putting them together. However, actual perceptual experience is coordinated: one perceives wine as both dark & sweet. In order khổng lồ explain this, Aristotle says that they must be coordinated by the central sense, which is probably located in the body’s central organ, the heart. When one is awake, and the external sense organs are functioning normally, they are coordinated in the heart to discern reality as being the way it is (Sens.448b31–449a22).

Aristotle claims that one hears that one hears và sees that one sees (DA 425b12–17). Though there is a puzzle as to lớn whether such higher-order seeing is due to lớn sight itself or to lớn the central perceptual power nguồn (compare On Sleep 455a3–26), the higher-order perception counts as an awareness of how the perceptual nguồn grasps an object in the world. Though later philosophers named this higher-order perception “consciousness” và argued that it could be separated from an actualized perception of a real object, for Aristotle it is intrinsically dependent on the first-order grasp of an object (Nakahata 2014, 109–110). Indeed, Aristotle describes perceptual powers as being potentially like the perceptual object in actuality (DA 418a3–5) and goes so far as to say that the activity of the external object and that of the perceptual power nguồn are one, though what it is lớn be each one is different (DA 425b26–27). Thus, consciousness seems khổng lồ be a property that arises automatically when perception is activated.

In at least some animals, the perceptual powers give rise lớn other psychological powers that are not themselves perceptual in a strict sense. In one simple case, the perception of a màu sắc is altered by its surroundings, that is, by how it is illuminated and by the other colors in one’s field of vision. Far from assuming the constancy of perception, Aristotle notes that under such circumstances, one color can take th