Epicurus’ theory of knowledge was not regarded as particularly impressive; indeed it was widely regarded as hideously crude. Later Epicureans, however, did develop interesting analogues of what we think of as issues of induction – how, from a number of particular observations, we can come to make justifiable generalizations about all occurrences of this kind of thing. Are we justified, for example (‘we’ being Epicurean philosophers living in Italy) in inferring that because all the humans we have observed are mortal, so are humans in hitherto undiscovered countries, such as Britain? (If there are any humans there, adds Philodemus, the philosopher whose example this is.)
Empiricist theories of knowledge, like an emphasis on the knower’s relation to particular facts, are the minority stream in ancient epistemology. What emerges from even a cursory survey of ancient concerns with knowledge, however, is the width and diversity of approaches. A student of epistemology in the ancient world would find a number of challenging theories and an extensive tradition of debate. She would find several ways of understanding knowledge: theories about wisdom and theories about apprehension of particular facts, theories privileging abstract reasoning and theories privileging the basic reports of the senses. She would also find extensive engagement not just with knowledge, but more generally with problems of belief and the powers of reasoning, both positive and negative.
Chapter 5
Logic and reality
If you specialize in philosophy at university, you discover that there are some skills you have to acquire, and topics you have to cover, in order to become competent in the subject. You will have to do some courses in logic and critical thinking, and cover topics in metaphysics, epistemology (and possibly philosophy of science), and in ethics, political philosophy (and possibly aesthetics). You may also have to do some history of philosophy, which will almost certainly be done in a way critical of philosophers, past and present, in what are seen as ‘other’ traditions, although philosophers in what is seen as ‘your’ tradition will be treated more respectfully.
In the ancient world things were not so different. After the establishment of Plato’s Academy, philosophical schools devoted to different philosophical traditions were the major places where philosophy was learnt, taught and passed on. Wealthy individuals might have philosophy tutors in their homes, but these would typically have been trained in some philosophical school. Each school would belong to a definite tradition, within which certain texts (typically Aristotle’s, or the Stoics’) were privileged. And from fairly early on the philosophical curriculum consisted of three parts: logic, physics and ethics. This happened early enough for it to be ascribed (unconvincingly) to Plato, though it is clear that neither Plato nor Aristotle wrote with such a curriculum in mind; it fits the interests of later schools, like the Stoics and Epicureans, far better. So far we have looked at an important topic in the ethics part of the curriculum, and also at theory of knowledge, which was considered part of logic, since logic was construed broadly, so as to cover what we call epistemology and philosophy of language. But there was also logic as we generally understand the term, more narrowly. And there is the topic that sounds oddest to us, ‘physics’.
Why is logic needed as part of philosophy? This topic was controversial then as now, some holding that logic was a part of philosophy in its own right, others that it was only a ‘tool’ that we use in order to improve our study of philosophy proper. Either way, we need logic to ensure that our arguments are sound ones, with no lurking fallacies for opponents to exploit, and also to enable us to detect weaknesses in the ways our opponents argue. In ancient philosophy logic has the function of sustaining philosophical truths and demolishing philosophical mistakes. Logic developed for its own sake was often regarded as a potential distraction from the central concerns of philosophy.
Logic is one of the more impressive achievements of Aristotle. Finding no given systematic techniques for classifying and distinguishing arguments that just persuade people from arguments which lead to true conclusions by valid inferences (and also finding, as today, many influential people glorying in conflating the two), Aristotle systematized the notion of valid argument and constructed an extensive logical system.
The centre of Aristotle’s logic is the idea of a deduction, in Greek sullogismos. He defines it quite generally: a deduction is an argument in which, some things having been laid down, something other than the things laid down comes about by necessity, because these things are so. More formally, the conclusion of a deduction follows necessarily from the premisses. Aristotle adds that the conclusion must be something different from the premisses; hence he is not trying to capture what modern logicians are after when they hold that ‘If p then p’ is a valid argument. He also holds that the truth of the conclusion must come about in a way that is through the truth of the premisses, thus excluding redundant premisses making no contribution in establishing the truth of the conclusion. Here too he diverges from modern notions of purely formal inference. There has been a large amount of (unsettled) modern discussion as to what Aristotelian deductions are, in terms of modern formal logic, and hence as to how his logic should be classified.
In modern terms Aristotle’s is only a fragment of logic, since, despite the wide scope of his definition of a deduction, he systematically studies only a much narrower range of deductions, those that have come to be known as Aristotelian syllogisms. He considers statements, positive and negative, that have the form of claiming that a predicate P, ‘belongs to’ or does not ‘belong to’ a subject S, in all, some or no cases. (As developed since the Middle Ages, these statements take the more familiar form of ‘All Ss are P,’ Some Ss are P,’Some Ss are not P, and ‘No Ss are P’.) Aristotle’s greatest contribution is the use of schematic letters, which enables him to study the form of an argument regardless of its particular content. He systematizes the ways in which two statements in one of these forms, which share a common term (the ‘middle’ term) lead to a conclusion. Some of these combinations will give valid arguments, others not. Aristotle devotes great ingenuity to showing which forms are valid, and which are not. (He also begins to develop a system of ‘modal logic’, that is, a logic of statements modified by ‘necessarily’, ‘possibly’ and so on, but less successfully.)