Aristotle calls all these investigations sciences (ἐπιστῆμαι): but he also uses the term “sciences” in a narrower sense in consequence of a classification of their objects, which pervades his writings, into things necessary and things contingent, as follows.—
(A) The necessary (τὸ μὴ ἐνδεχόμενον ἄλλως ἔχειν), what must be; subdivided into:—
(1) Absolutely (ἁπλῶς), e.g. the mathematical.
(2) Hypothetically (ἐξ ὑποθέσεως), e.g. matter necessary as means to an end.
(B) The contingent (τὸ ἐνδεχόμενον ἄλλως ἔχειν), what may be; subdivided into:—
(1) The usual (τὸ ὡς ἐπὶ τὸ πολύ) or natural (τὸ φυσικόν), e.g. a man grows grey.
(2) The accidental (τὸ κατὰ συμβεβηκός), e.g. a man sits or not.
Now, according to Aristotle, science in the narrow sense is concerned only with the absolutely necessary (E.N. iii. 3), and in the classification would stop at mathematics, which we still call exact science: in the wide sense, on the other hand, it extends to the whole of the necessary and to the usual contingent, but excludes the accidental (Met. Ε 2), and would in the classification include not only metaphysics and mathematics, but also physics, ethics, economics, politics, necessary and fine art; or in short all speculative, practical and productive thinking of a systematic kind. Hence the Posterior Analytics, which is Aristotle’s authoritative logic of science, is of peculiar interest because, after beginning by defining science as investigating necessary objects from necessary principles (i. 4), it proceeds to say that it is either of the necessary or of the usual though not of the accidental (i. 29), and to admit that its principles are some necessary and some contingent (i. 32, 88 b 7). Philosophy (φιλοςοφία) also is used by him in a similar manner. Though occasionally he means by it primary philosophy (Met. Γ 2-3, Κ 3), more frequently he extends it to all three speculative philosophies (Ε 1, 1026 a 18, τρεῖς ἂν εἶεν φιλοσοφίαι θεωρητικαί, μαθηματική, φυσική, θεολογική), and to all three practical philosophies, as we see from the constant use of the phrase “political philosopher” in the Ethics; and in short applies it to all sciences except productive science or art. With him, as with the Greeks generally, the problems of philosophy are the nature and origin of being and of good: it is not as with too many of us a mere science of mind.
Aristotle’s view of thinking in science and philosophy is essentially comprehensive; but it is not so wide as to become indefinite. According to him, science at its widest selects a special subject, e.g. number in arithmetic, magnitude in geometry, stars in astronomy, a man’s good in ethics; concentrates itself on the causes and appropriate principles of its subject, especially the definition of the subject and its species by their essences or formal causes; and after an inductive intelligence of those principles proceeds by a deductive demonstration from definitions to consequences: philosophy is simply a desire of this definite knowledge of causes and effects. Beyond philosophy, not beyond science, there is art; and beyond philosophy and science there is history, the description of facts preparatory to philosophy, the investigation of causes (cf. Pr. An. i. 30); and this may be natural history, preparatory to natural philosophy, as in the History of Animals preparatory to the De Partibus Animalium, or what we call civil history, preparatory to political philosophy, as in the 158 Constitutions more or less preparatory to the Politics.
Wide as is all his knowledge of facts and causes, it does not appear to Aristotle to be the whole of learning and the show of it. Beyond knowledge lies opinion, beyond discovery disputation, beyond philosophy and science dialectic between man and man, which was much practised by the Greeks in the dialogues of Socrates, Plato, the Megarians and Aristotle himself in his early manhood. With Plato, who thought that the interrogation of man is the best instrument of truth, dialectic was exaggerated into a universal science of everything that is. Aristotle, on the other hand, learnt to distinguish dialectic (διαλεκτική) from science (ἐπιστήμη); in that it has no definite subject, else it would not ask questions (Post. An. i. 11, 77 a 31-33); in that for appropriate principles it substitutes the probabilities of authority (τὰ ἔνδοξα) which are the opinions of all, or of the majority, or of the wise (Top. i. 1, 100 b 21-23); and in that it is not like science a deduction from true and primary principles of a definite subject to true consequences, but a deduction from opinion to opinion, which may be true or false. Sophistry appeared to him to be like it, except that it is a fallacious deduction either from merely apparent probabilities in its matter or itself merely apparently syllogistic in its form (cf. Topics, i. 1). Moreover, he compared dialectic and sophistry, on account of their generality, with primary philosophy in the Metaphysics (Γ 2, 1004 b 17-26); to the effect that all three concern themselves with all things, but that about everything metaphysics is scientific, dialectic tentative, sophistry apparent, not real. He means that a sophist like Protagoras will teach superficially anything as wisdom for money; and that even a dialectician like Plato will write a dialogue, such as the Republic, nominally about justice, but really about all things from the generality of the form of good, instead of from appropriate moral principles; but that a primary philosopher selects as a definite subject all things as such without interfering with the special sciences of different things each in its kind (Met. Γ 1), and investigates the axioms or common principles of things as things (ib. 3), without pretending, like Plato, to deduce from any common principle the special principles of each science (Post. An. i. 9, 32). Aristotle at once maintains the primacy of metaphysics and vindicates the independence of the special sciences. He is at the same time the only Greek philosopher who clearly discriminated discovery and disputation, science and dialectic, the knowledge of a definite subject from its appropriate principles and the discussion of anything whatever from opinions and authority. On one side he places science and philosophy, on the other dialectic and sophistry.