A study in philosophical logic of the meaning of 'true'. Dr Williams demonstrates the shortcomings of various analyses which interpret 'true' as a predicate or truth as a relational property, and clears up a number of important points about propositions, quantification, definite descriptions and correspondence. This 'deflationary metaphysics' is interwoven with a positive theory of his own, which seeks to develop ideas about the late Arthur Prior. The work is marked throughout by great clarity, precision and thoroughness.

Philosophers have met with many problems in discussing the interconnected concepts being, identity, and truth, and have advanced many theories to deal with them. Professor Williams argues that most of these problems and theories result from an inadequate appreciation of the ways in which the words `be', `same', and `true' work. By means of linguistic analysis he shows that being and truth are not properties, and identity is not a relation. He is thus able to demystify a number of metaphysical issues concerning the meaning of the word `I', the relation between the mental and the physical, objects of thought, times and places, and the nature of reality. Williams presents his views clearly, with a minimum of technicality, and with rich and apt examples, so that they will be accessible to readers not versed in symbolic logic.

The concept of identity has been seen to lead to paradox: we cannot truly and usefully say that a thing is the same either as itself or as something else. This book is a full examination of this paradox in philosophical logic, and of its implications for the philosophy of mathematics, the philosphy of mind, and relativism about identity. The author's account involves detailed discussion of the views of Wittgenstein, Russell, Frege, and Hintikka.

These chapters of Aristotle's treatise are about physical interactions. In his innovative commentary, Philoponus discusses Aristotle's idea that certain qualities of the elements are basic. In what way are they basic? he asks. To what extent can the other qualities be reduced to the basic ones? And if the other qualities depend on the basic ones, how is it that they can vary independently of each other when the basic qualities change? Philoponus develops the idea that the other qualities merely supervene on the basic ones, rather than resulting from them. Moreover, physical qualities admit of different ranges of variation, and so have different thresholds at which they appear or disappear. Philoponus also discusses Aristotle's idea that the elements and their basic qualities survive potentially when mixed together. He explains this by drawing a third sense of 'potential' out of Aristotle's texts to take the place of the two senses which Aristotle explicitly recognises. Philoponus adds further restrictions to Aristotle's principles of causation. Black can contaminate white, but the black in ebony does not have the right matter for affecting the white of milk. He asks why fluids can affect each other more easily than solids. In every case, Philoponus takes Aristotle's discussions further, and his ideas on the dependence of some qualities on others are very relevant to the continuing philosophical debate on the subject.

The first five chapters of Aristotle's De Generatione et Corruptione distinguish creation and destruction from mere qualitative change and from growth. They include a fascinating debate about the atomists' analysis of creation and destruction as due to the rearrangement of indivisible atoms. Aristotle's rival belief in the infinite divisibility of matter is explained and defended against the atomists' powerful attack on infinite divisibility. But what inspired Philoponus most in his commentary is the topic of organic growth. How does it take place without ingested matter getting into the same place as the growing body? And how is personal identity preserved, if our matter is always in flux, and our form depends on our matter? If we do not depend on the persistence of matter why are we not immortal? Analogous problems of identity arise also for inanimate beings. Philoponus draws out a brief remark of Aristotle's to show that cause need not be like effect. For example, what makes something hard may be cold, not hard. This goes against a persistent philosophical prejudice, but Philoponus makes it plausible that Aristotle recognized this truth. These topics of identity over time and the principles of causation are still matters of intense discussion.