If you think that a proposition can have more than one contradictory, or can have none, then you need read no further. What I will show is that if then It is not obvious that this must be so. If p1 and p2 are distinct but logically equivalent, it might appear that their contradictories, q1 and q2, should also be distinct though logically equivalent. In traditional logic, a pair of propositions which satisfy (3)(i) alone are called contraries, and a pair (...) which satisfy (3)(ii) alone are called sub-contraries.2 The relation of contradictoriness defined by (3) is clearly symmetrical: Let p1 and p2 be two propositions which are logically equivalent, and assume (1). Then p1 has a contradictory, q. We first show that Suppose p2 and q were both true. Then, since p1 and p2 are logically equivalent, p1 and q would both be true. But p1 and q are contradictories, so, by (3)(i) p1 and q cannot both be true. We next show that By (3)(ii) at least one of p1 and q must be true. So, since p1 and p2 are logically equivalent, at least one of p2 and q must be true. From (5) and (6) it follows that p2 and q are contradictories, so by (4) From (7) and (1) we have that p1 and p2 are identical; and since all that was assumed about them was that they are logically equivalent, (2) follows. (shrink)

Aristotle's treatise De Interpretatione is one of his central works; it continues to be the focus of much attention and debate. C. W. A. Whitaker presents the first systematic study of this work, and offers a radical new view of its aims, its structure, and its place in Aristotle's system, basing this view upon a detailed chapter-by-chapter analysis.By treating the work systematically, rather than concentrating on certain selected passages, Whitaker is able to show that, contrary to traditional opinion, it forms (...) an organized and coherent whole. He argues that the De Interpretatione is intended to provide the underpinning for dialectic, the system of argument by question and answer set out in Aristotle's Topics; and he rejects the traditional view that the De Interpretatione concerns the assertion and is oriented towards the formal logic of the Prior Analytics. In doing so, he sheds valuable new light on some of Aristotle's most famous texts. (shrink)

Aristotle's theory of truth, which has been the most influential account of the concept of truth from Antiquity onwards, spans several areas of philosophy: philosophy of language, logic, ontology and epistemology. In this 2004 book, Paolo Crivelli discusses all the main aspects of Aristotle's views on truth and falsehood. He analyses in detail the main relevant passages, addresses some well-known problems of Aristotelian semantics, and assesses Aristotle's theory from the point of view of modern analytic philosophy. In the process he (...) discusses most of the literature on Aristotle's semantic theory to have appeared in the last two centuries. His book vindicates and clarifies the often repeated claim that Aristotle's is a correspondence theory of truth. It will be of interest to a wide range of readers working in both ancient philosophy and modern philosophy of language. (shrink)