Aristotle was born of a well-to-do family in the Macedonian town of Stagira in 384 BCE. His father, Nicomachus, was a physician who died when Aristotle was young. In 367, when Aristotle was seventeen, his uncle, Proxenus, sent him to Athens to study at Plato’s Academy. There he remained, first as a pupil, later as an associate, for the next twenty years.
When Plato died in 347, the Academy came under the control of his nephew Speusippus, who favored mathematical aspects of Platonism that Aristotle, who was more interested in biology, found uncongenial. Perhaps for this reason - but more likely because of growing anti-Macedonian sentiment in Athens - Aristotle decided to leave. He accepted the invitation of Hermeias, his friend and a former fellow student in the Academy, to join his philosophical circle on the coast of Asia Minor in Assos, where Hermeias (a former slave) had become ruler. Aristotle remained there for three years. During this period he married Hermeias’s niece, Pythias, with whom he had a daughter, also named Pythias.
In 345, Aristotle moved to Mytilene, on the nearby island of Lesbos, where he joined another former Academic, Theophrastus, who was a native of the island. Theophrastus, at first Aristotle’s pupil and then his closest colleague, remained associated with him until Aristotle’s death. While they were on Lesbos the biological research of Aristotle and Theophrastus flourished. In 343, Philip of Macedon invited Aristotle to his court to serve as tutor to his son Alexander, then thirteen years old. What instruction Aristotle gave to the young man who was to become Alexander the Great is not known, but it seems likely that Aristotle’s own interest in politics increased during his stay at the Macedonian court. In 340 Alexander was appointed regent for his father and his studies with Aristotle ended.
The events of the next five years are uncertain. Perhaps Aristotle stayed at the court; perhaps he went back to Stagira. But in 335, after the death of Philip, he returned to Athens for his second long sojourn. Just outside the city he rented some buildings and established his own school, the Lyceum, where he lectured, wrote, and discussed philosophy with his pupils and associates. Under his direction, they carried out research on biological and other philosophical and scientific topics. Theophrastus worked on botany, Aristoxenus on music; Eudemus wrote a history of mathematics and astronomy, Meno of medicine, and Theophrastus of physics, cosmology, and psychology. In addition, Aristotle and his group produced a monumental account of the constitutions of 158 Greek city-states - an account Aristotle draws on in his own Politics.
While he was in Athens, Aristotle’s wife Pythias died. He subsequently began a union with a woman named Herpyllis, like Aristotle a native of Stagira. Although they apparently never married, they had a son, whom they named Nicomachus, after Aristotle’s father.
Aristotle’s work during his twelve or thirteen years at the Lyceum was prodigious. Most of his surviving works were probably written during this period. But when Alexander died in 323, Athens once again became a hostile environment for a Macedonian, and Aristotle was accused of impiety (the same charge that had been leveled against both Anaxagoras and Socrates). Leaving the Lyceum in the hands of Theophrastus, Aristotle fled northward to the Macedonian stronghold of Chalcis (his mother’s birthplace); he is said to have remarked that he would “not allow the Athenians to sin twice against philosophy.” Removed from the cultural center of Athens, he lamented his isolation and died in 322 at the age of sixty-two.
Of Aristotle’s writings, only about one fifth to one quarter have survived. Still, the great variety of subjects that they cover provides a good indication of the range and depth of his interests. The notorious difficulty these writings pose for the contemporary reader is in part explained by the nature of the works themselves. Far from being polished pieces of prose intended for publication, they are for the most part working papers and lecture notes, terse and compressed often to the point of unintelligibility. (Ancient sources tell us that in his published works - now lost - Aristotle displayed an exemplary literary style, and there are occasional glimpses of it in the surviving works.)
Aristotle was above all driven by a desire for knowledge and understanding in every possible realm. His works are teeming with detailed observations about the natural world as well as abstract speculations of the most general sort. As both a scientist and a philosopher, Aristotle could easily make the transition from describing the feeding behavior of eels and limpets to theorizing about the divine intellect that is the uncaused cause of everything else in the universe. But his philosophical and scientific interests are rooted in the natural world - about one quarter of the surviving works deal with topics in biology. This he combined with an unshakeable confidence in the ability of the human mind, aided by the system of deductive logic he invented and by close and detailed observation of natural phenomena, to comprehend the fundamental nature of objective reality.
Aristotle did not suppose that he was the first person to attempt this task. He was a keen student of the writings of his scientific and philosophical predecessors. The influence of Plato’s thought is apparent throughout Aristotle’s works, even where he disagrees with his teacher most. He pays a great deal of attention to the Presocratics, seldom agreeing with them, but often crediting them with important (albeit usually partial) insights. His typical approach to a subject is to review its history and then, making what use he can of the received opinions, to set out his own account. Often his position is a kind of compromise that incorporates the best features while avoiding the excesses of rival schemes that are too extreme.
All of the sciences (epistêmai, literally “knowledges”) can be divided into three branches: theoretical, practical, and productive. Whereas practical sciences, such as ethics and politics, are concerned with human action, and productive sciences with making things, theoretical sciences, such as theology, mathematics, and the natural sciences, aim at truth and are pursued for their own sake. Aristotle was unique in pursuing all three. His Rhetoric and Poetics, which provide the foundation for the study of speech and literary theory, are his contributions to the productive sciences. The Ethics and Politics are devoted to the practical sciences. In the remainder of his works, Aristotle directs his attention to the theoretical sciences.
A science, according to Aristotle, can be set out as an axiomatic system in which necessary first principles lead by inexorable deductive inferences to all of the truths about the subject matter of the science (Posterior Analytics I.6). Some of these first principles are peculiar to the science in question, as the definition of a straight line is to geometry. Some - such as the principle of noncontradiction - are so general that they are common to all the sciences (Metaphysics IV.3). Scientific knowledge is therefore demonstrative; what we know scientifically is what we can derive, directly or indirectly, from first principles that do not themselves require proof.
What, then, is the status of the first principles? They clearly cannot be known in the same way as the consequences derived from them, i.e., demonstratively, yet Aristotle is confident that they must be known - for how could knowledge be derived from what is not knowledge? They are, Aristotle tells us, grasped by the mind (Aristotle’s term is nous, usually translated as intuition or understanding). This way of putting the matter makes it seem as if an Aristotelian science is an entirely a priori enterprise in which reason alone grasps first principles and logic takes over from there to arrive at all of the truths of science. And Aristotle does say that it is dialectic - a process of deductive reasoning - that provides a path to first principles (Topics I.2).
It is clear, however, that Aristotle does not think that this alone is the way a scientist goes about acquiring his knowledge. For in his own scientific treatises, he does not begin by announcing the first principles and deducing their consequences. Rather, he sets out the puzzles the science is trying to solve and the observations that have been made and the opinions that have been held about them. Perhaps he thinks of the axiomatic presentation as a kind of ideal that is possible only for a completed science and is appropriate for teaching it rather than for making discoveries in it. As for the acquisition of first principles, Aristotle appeals to what sounds somewhat like an inductive procedure. Beginning with the perception of particulars, which are “better known to us,” and moving through memory and experience, we arrive at knowledge of universals, which are “better known in themselves” (Posterior Analytics II.19, Metaphysics I.1). Aristotle’s approach thus seems to combine features of both rationalism and empiricism.
Each of the special sciences studies some particular realm of being, some part of what there is. But there is also, Aristotle maintains (Metaphysics IV.1), a more general study of what there is, a study of being qua being. (‘Qua’ is a technical expression Aristotle uses to indicate an aspect under which something is to be considered.) The study of being qua being concerns the most general class of things, viz., everything that exists. And it studies them under their most general aspect, namely, as things that exist. It thus raises the question of what it is for something to exist.
Now on Aristotle’s view what it is for a horse to exist is different in kind from what it is for whiteness or courage to exist. “Being,” he tells us, “is said in many ways” (Metaphysics IV.2). So it might seem that there could not be a unified answer to question of what it is for something in general to exist. But he also thinks that there is a connection among these modes of being (or senses of ‘exist’) which is deep enough to make a unified answer possible. The existence of whiteness is derivative; there is such a thing as whiteness because something, for example some horse, is white. Whiteness is not an independent entity, capable of existing on its own. Horses and other biological specimens, on the other hand, are independent entities. Such independently existing entities Aristotle called substances. (The Greek word traditionally translated as ‘substance’ may with equal plausibility be rendered ‘basic reality’.) The existence of everything else is somehow dependent on its relation to substances. Hence Aristotle tells us that the ancient and perennial question “What is being?” really comes down to the question “What is substance?” (Metaphysics VII.1).
Substances, then, are the most fundamental realities. But not all of Aristotle’s predecessors would have agreed with him about what the substances are. Empedocles would have said that the four elements are the only substances; Democritus would call the atoms substances; for Plato, the substances are his independently existing and immaterial forms. Much of Aristotle’s Metaphysics is spent trying to steer a middle course between the materialism of these Presocratics, on the one hand, and Platonism, on the other. How successful he is in this effort - and indeed, even the precise details of his solution - are matters of dispute.
In his earliest ontological writings, Aristotle maintains that individual biological specimens - this man, or that tree - are the primary substances (Categories 5). The species to which they belong, man and tree, are substances in a secondary sense. But he subsequently (Metaphysics VII-VIII) begins to raise the question of what it is that makes this man or that tree a substance - what the substance of these things is, as he puts it. He intimates that the answer to this question will tell us what primary substance is. His convoluted and difficult investigation of this question leads him to the conclusion that it is form or essence that is primary substance. This suggests a tilt in the direction of Platonism, but Aristotle insists that his answer is different from Plato’s. For on his view Platonic forms are separate from and independent of their material instantiations, whereas Aristotelian essences in some sense are not. Still, much remains unclear about Aristotle’s answer. For example, there is no consensus among scholars about whether Aristotle thought of essences as being particular (so that each individual horse has its own unique essence) or specific (in which case the essence of all horses will be the same).
Aristotle’s universe is finite, eternal, and geocentric: a stationary earth surrounded by concentric spheres that carry the sun, moon, planets, and stars in their circular orbits about the earth. Everything below the sphere of the moon is made of four fundamental elements - earth, water, air, and fire - that interact and are capable of transforming into one another. Each element is characterized by a pair of properties from among the contraries hot, cold, wet, and dry. Earth is cold and dry, water cold and wet, air hot and wet, fire hot and dry. The heavenly bodies are made of a different kind of matter altogether, a fifth element (“quintessence”). Each element has a natural place and a natural movement. The four sublunary elements tend to move in a straight line, earth downward toward the center of the universe, fire toward the extreme, and air and water toward intermediate places. Once in its natural place, each of these four remains at rest unless something else causes it to move. The natural movement of the fifth element in the heavens is circular and eternal. All of this movement and change is ultimately explained in terms of an “unmoved mover” - a cause of change that is itself uncaused and outside of the universe (De Caelo I-III, On Generation and Corruption II.4, Physics VIII.6, Metaphysics XII.6-9).
It is the job of natural science to study things whose nature it is to undergo change. In the face of influential Parmenidean arguments against the possibility of change, Aristotle attempted to set out a framework that would make change intelligible. Every change involves three essential ingredients: a pair of opposed characteristics or states (from which and to which, respectively, the change occurs) and a subject which underlies the change and persists through it. Schematically, every change, every case of “coming to be,” can be described in this way: something, x, goes from being F to being not F, or vice versa. A musician comes to be because a man goes from being unmusical to being musical; a statue comes to be because some shapeless bronze takes on a definite form. Contrary to what Parmenides argued, coming to be does not involve getting something from nothing; it involves getting something which is F from something which is (among other things) not F (Physics I.7-9).
These are the necessary preconditions for change. But what is change? Aristotle defines it in terms of his concepts of actuality and potentiality. Change, he tells us, is “the actuality of what is potentially, qua such” (Physics III.1). The process of building a house, for example, is the actuality of the buildable materials, qua buildable. The materials that are potentially a house are already actual even before the building begins - they are bricks and boards, etc. So the actuality with which Aristotle identifies change is that of the bricks and boards not qua bricks and boards, but qua buildable. It is precisely when the house is in the process of being built that this potentiality of the materials actually (and not merely potentially) exists as a potentiality. Once the process is completed, that potentiality has been replaced by a corresponding actuality, that of the completed house. The precise meaning of Aristotle’s definition of change is a subject of scholarly debate. For present purposes it is sufficient to note that in undergoing change a thing is actualizing a potentiality that it already has even before it changes. It is thus already part of its nature to be able to undergo change of that sort.
It is the job of a theoretical science to explain things, and that means that it must answer “Why?” questions. To answer such a question is to give a cause. (Aristotle’s word is aition; ‘explanation’ is an equally appropriate translation.) But ‘cause’ is “said in many ways” (Physics II.3). In one sense, the cause of something is the material out of which it comes to be (material cause). In another sense, it is the form or essence stated in the definition of the thing (formal cause). In a third, it is the source of change or stability (efficient cause). In a fourth, it is the end (telos), what the thing is for (final cause). Note that it is not just events that have causes, in Aristotle’s view; houses and tigers have causes just as much as eclipses and explosions do. Note also that there can be more than one cause of the same thing (e.g., bronze is the material cause of a statue, whereas a certain shape is its formal cause). Indeed, two things may be causes of one another, as exercise is the (efficient) cause of health, and health is the (final) cause of exercise.
A complete account of something will mention all of the causes that are appropriate to it. Artifacts clearly have causes in all four senses: a house is made of wood, by a builder, with a form and structure suitable to provide a shelter for human beings and their possessions. Mathematical objects, since they do not undergo change, have no efficient or final causes. Natural objects, such as plants and animals, clearly have the first three kinds of cause, for they come into being, are composed of matter (ultimately of the four elements), and have essential natures. But are there final causes in nature? Aristotle maintains, notoriously, that there are (Physics II.8, Parts of Animals I.1). His teleological account of nature is central to his entire philosophical system.
His position here may strike us as an aberration if we identify final causes with conscious intentions. The final causes of artifacts are found in the minds of the artisans who made them; they are in that sense external to the artifacts themselves. (It is for this reason that artifacts do not count for Aristotle as genuine substances. Lacking final causes that are internal to them, they do not engage in activity of their own, and hence they have no essence, strictly speaking.) But final causes in nature are not like this at all. Rather, Aristotle’s idea is that the final causes of natural objects are internal to those objects. Consider the living creatures that populate the natural world. They behave in certain characteristic ways: they interact with their environment, nourish themselves, reproduce. Their being is defined by these functions and these characteristic activities. The parts of which they are composed enable them to fulfill these functions more or less successfully. It is not by accident that animals have teeth or eyes; these organs clearly have functions - they are for something. And what they are for is typically beneficial for the organism; they enable it to survive and to engage in the activities that define its being. It is function and activity, not purpose, that Aristotle claims to discern in nature.
This understanding of Aristotle’s teleology helps to explain why he believes that final, formal, and efficient causes often coincide (Physics II.7). For just as the various parts and organs of an animal contribute toward its well-being and survival, the telos of the animal itself is to be a good (i.e., successful) specimen of its kind. So the final cause of a tiger is just to be a tiger, as specified in its formal cause (i.e., its definition). The coincidence of the efficient cause with the final and the formal can be seen most easily in the case of reproduction and development. The efficient cause of a tiger cub is a tiger (in Aristotle’s view, its father). As the cub grows, its process of development tends almost invariably (in the normal case - occasionally things go awry) toward the same outcome: a mature individual that, like its parents, satisfies the definition of a tiger.
The being of a living thing is thus inextricably bound up in its being alive and living the life that a thing of its kind lives. What is it that differentiates the living from the nonliving? Aristotle’s answer is: the presence of the soul (psuchê). We notice immediately an important difference between this and later conceptions of soul: psuchê for Aristotle is linked with life in general, rather than with mind, thought, or personality in particular. All living things have souls. But there are different degrees or levels of soul, associated with different capacities or functions. At the most fundamental level is the nutritive soul, the kind of soul common to all living things; for all plants and animals have the capacity to take in nourishment. Higher levels of soul account for the appetitive, locomotive, and perceptive capacities of humans and other animals. At the highest level is the rational soul, peculiar to humans.
But what is the soul? Aristotle defines it to be the form of the body. More precisely, it is the “first actuality of a natural body that has life potentially” (De Anima II.1). The term ‘first actuality’ needs some explanation. As Aristotle uses the expression, a first actuality is not itself an activity or bit of behavior (a ‘second actuality’), but a capacity or ability to act or to behave. It is thus a kind of potentiality (a ‘second potentiality’), an organizing principle that enables a living thing to go about the business of living. To have a soul, then, is to have the capacity to engage in certain characteristic activities. In the most general case, it is the capacity to metabolize. For higher levels of soul, it is the capacity to move about, to have desires and to fulfill them, to perceive, to contemplate.
The soul is therefore neither a material part of an animal, nor some immaterial thing capable of existing in separation from the body. For the soul is a set of capacities that a living thing has, and these capacities are incapable of existing on their own - they are the capacities of a living thing. Aristotle thus resists both a materialistic conception of the soul as some kind of bodily part and a Platonic conception which holds the soul to be independent of and, indeed, impeded by the body.
Much of Aristotle’s discussion of the soul concerns the topic of sense-perception (De Anima II.5-12). He discusses the physiology of each of the five senses in detail and defines perception in general as the reception in the soul of the perceptible form of an external object. His account of thought to some extent mirrors what he says about perception. In thinking the mind takes on the intelligible form of its object and in so doing becomes, in a sense, identical to it. Aristotle thereby avoids the problem of having somehow to relate a mental representation to an object external to the mind. But thought differs from perception in an important respect: whereas there are sense organs, there is, for Aristotle, no organ of thought (De Anima III.4). For this reason he holds that thought, unlike other psychic functions, is somehow separable from the body. It is not clear how well this aspect of Aristotle’s theory can be made to harmonize with his otherwise hylomorphic conception of the soul.
Thus far we have looked at some of Aristotle’s answers to the questions of the theoretical sciences. As we shall see, his approach to the practical sciences builds on those answers. The central question of ethics is how to live, i.e., what the good life is, and Aristotle’s answer is basically naturalistic. He takes it to be uncontroversial that all of our actions are aimed at some good. So the good, he reasons, is “that at which all things aim” (Nicomachean Ethics I.1). And what is this good? It must be something that is chosen for its own sake, and not for the sake of something else. Aristotle’s answer is that it is happiness (eudaimonia) in the sense of well-being or flourishing. (It would be a mistake to think of happiness here in the narrow sense of a kind of mental or emotional state.) The well-being of a thing consists in its fulfilling its basic functions and performing its characteristic activities. Human happiness or well-being, then, consists in fulfilling the functions and performing the activities that define life for human beings. All animals nourish themselves, and grow, and perceive. What is distinctively human is the rational faculty, and that is what determines our well-being. Eudaimonia is therefore an “activity of soul in accordance with virtue or excellence (aretê)” (Nicomachean Ethics I.7). We flourish, then, when we do well the things that are distinctively human.
The remainder of Aristotle’s Ethics consists of an unpacking of this basic conception of eudaimonia. He distinguishes virtues of character from intellectual virtues, and discusses all of them in detail (Nicomachean Ethics II-VI). Intellectual virtues are excellences of the rational element in the soul. But the irrational element also has an aspect that is rational in that it is capable of being persuaded by reason, and the excellences of this part of the soul are virtues of character, or moral virtues (Nicomachean Ethics I.13). Such a virtue is a disposition to choose actions that are intermediate between the extremes of excess and deficiency. (For example, courage is a mean between cowardice and rashness.) These choices must be made in accordance with reason, as would be determined by a person of practical wisdom. So possession of the moral virtues implies the possession of the intellectual virtues, as well, since practical wisdom is an intellectual virtue. Of the intellectual virtues, the highest is that of theoretical contemplation. This, finally, is the activity of the soul with which Aristotle identifies the highest form of eudaimonia (Nicomachean Ethics X.7).
In Aristotle’s view, politics is continuous with ethics. For just as it is part of human nature to seek happiness, it is also part of human nature to live in communities. We are, Aristotle asserts, social animals (Politics I.2). The state is the highest form of community; it is a natural entity, and does not exist merely by convention. (The kind of state Aristotle has in mind is the relatively small city-state of fourth century Greece.) Plato had argued that the structure of the soul was like that of the state, with different psychic functions corresponding to different classes of citizens. For Aristotle, the analogy works the other way around. The state has a proper function and a nature in the same way that an individual organism does. Hence, to say what a state is we must determine what its proper function is.
Aristotle believes that a state exists for the sake of the good or happy life, so that the best form of government will be one which promotes the well-being of all of its citizens; and he goes on, after considering a variety of alternatives, to describe such a state in considerable detail (Politics VII). In his emphasis on the rule of law and the role of a constitution in defining a state, Aristotle’s ideas are still timely today. There are other aspects of his thought, however, such as his belief that there are natural rulers and natural slaves, that the contemporary reader will no doubt find repugnant.
Aristotle has had a profound influence on the history of philosophy. From late antiquity through the middle ages, it was standard procedure for philosophers to couch their own writings in the form of commentaries on his works. His logic was so thoroughly accepted that the subject remained virtually unchanged for the next two millennia. His concepts of subject and predicate, matter and form, essence and accident, species and genus, among others, have become a standard part of the philosophical vernacular. Although many of his ideas have been discredited or superseded, much of what he has to say remains relevant to issues of vital contemporary interest. In terms of the breadth of his intellectual curiosity and the vastness of his influence, Aristotle is without equal in the history of human thought.
By S. Marc Cohen, Department of Philosophy, University of Washington.
From Readings in Ancient Greek Philosophy, Third Edition (Hackett: 2005), S. Marc Cohen, Patricia Curd, and C.D.C. Reeve, eds., pp. 645-654. © 2005, Hackett Publishing Company. Reprinted here by permission of Hackett Publishing Company, Indianapolis, IN.