ARISTOTLE

(b. 384 BCE, Stagira, Chalcidice, Greece—d. 322 BCE, Chalcis, Euboea)

Aristotle (Greek: Aristoteles) was an ancient Greek philosopher and scientist, and one of the greatest intellectual figures of Western history. He was the author of a philosophical and scientific system that became the framework and vehicle for both Christian Scholasticism and medieval Islamic philosophy. Aristotle’s intellectual range was vast, covering most of the sciences and many of the arts, including biology, botany, chemistry, ethics, history, logic, metaphysics, rhetoric, philosophy of mind, philosophy of science, physics, poetics, political theory, psychology, and zoology. He was the founder of formal logic, devising for it a finished system that for centuries was regarded as the sum of the discipline. Aristotle also pioneered the study of zoology, both observational and theoretical, in which some of his work remained unsurpassed until the 19th century. His writings in metaphysics

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This statue of Aristotle, the Greek philosopher who taught Alexander the

Great, stands in the Palazzo Spada in Rome. Popperfoto/Getty Images

and the philosophy of science continue to be studied, and his work remains a powerful current in contemporary philosophical debate.

Physics and Metaphysics

Aristotle divided the theoretical sciences into three groups: physics, mathematics, and theology. Physics as he understood it was equivalent to what would now be called “natural philosophy,” or the study of nature; in this sense it encompasses not only the modern field of physics but also biology, chemistry, geology, psychology, and even meteorology. Metaphysics, however, is notably absent from Aristotle’s classification; indeed, he never uses the word, which first appears in the posthumous catalog of his writings as a name for the works listed after the Physics. He does, however, recognize the branch of philosophy now called metaphysics. He calls it “first philosophy” and defines it as the discipline that studies “being as being.”

Aristotle’s contributions to the physical sciences are less impressive than his researches in the life sciences. In works such as On Generation and Corruption and On the Heavens, he presented a world-picture that included many features inherited from his pre-Socratic predecessors. From Empedocles (c. 490–430 BCE) he adopted the view that the universe is ultimately composed of different combinations of the four fundamental elements of earth, water, air, and fire. Each element is characterized by the possession of a unique pair of the four elementary qualities of heat, cold, wetness, and dryness: earth is cold and dry, water is cold and wet, air is hot and wet, and fire is hot and dry. Each element also has a natural place in an ordered cosmos, and each has an innate tendency to move toward this natural place. Thus, earthy solids naturally fall, while

fire, unless prevented, rises ever higher. Other motions of the elements are possible but are considered “violent.” (A relic of Aristotle’s distinction is preserved in the modernday contrast between natural and violent death.)

Aristotle’s vision of the cosmos also owes much to Plato’s dialogue Timaeus. As in that work, the Earth is at the centre of the universe, and around it the Moon, the Sun, and the other planets revolve in a succession of concentric crystalline spheres. The heavenly bodies are not compounds of the four terrestrial elements but are made up of a superior fifth element, or “quintessence.” In addition, the heavenly bodies have souls, or supernatural intellects, which guide them in their travels through the cosmos.

Even the best of Aristotle’s scientific work has now only a historical interest. The abiding value of treatises such as the Physics lies not in their particular scientific assertions but in their philosophical analyses of some of the concepts that pervade the physics of different eras— concepts such as place, time, causation, and determinism.

Philosophy of Science

In his Posterior Analytics, Aristotle applies the theory of the syllogism (a form of deductive reasoning) to scientific and epistemological ends (epistemology is the philosophy of the nature of knowledge). Scientific knowledge, he urges, must be built up out of demonstrations. A demonstration is a particular kind of syllogism, one whose premises can be traced back to principles that are true, necessary, universal, and immediately intuited. These first, self-evident principles are related to the conclusions of science as axioms are related to theorems: the axioms both necessitate and explain the truths that constitute a science. The most important axioms, Aristotle thought, would be those that define the proper subject matter of a science. Thus, among the axioms of geometry would be the definition of a triangle. For this reason much of the second book of the Posterior Analytics is devoted to definition.

The account of science in the Posterior Analytics is impressive, but it bears no resemblance to any of Aristotle’s own scientific works. Generations of scholars have tried in vain to find in his writings a single instance of a demonstrative syllogism. Moreover, the whole history of scientific endeavour contains no perfect instance of a demonstrative science.

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