My first encounter with David Wiggins’ thought occurred a few weeks before I took my undergraduate final examinations in Oxford in 1971. In Blackwell's Bookshop I came across a slim blue volume Identity and Spatio-Temporal Continuity. I purchased it and read it cover-to-cover the same day. It was immediately clear that this was contemporary writing in a different league from anything I had previously read on the topic.

That concise and tightly argued work, the seed of many books to follow, showed the first of three characteristics of David's writing that I want to highlight. This first property is the clustering and interaction of sharp and fundamental insights in philosophical logic about the level of objects, the relation of identity, and their involvement with sortals. The cluster includes the three crucial points that Leibniz’ Law is a non-negotiable and, properly understood, a completely obvious principle (‘as obvious as the Law of Non-Contradiction’ as David says on page 5 of the book); that it immediately excludes Geach's relativity of identity; and that the correct understanding of the role of sortals in identity is that x=y iff there is some sortal property F such that x is the same F as y. That last principle seemed to me back then on first reading, and still seems to me now, an enduring, fertile, and fundamental contribution to philosophy. It is a part of our canon.

A year later, in spring 1972, I met David at Harvard, where he was visiting for a semester and I was a Kennedy Scholar. I was truly a beginner in the subject, he was already a distinguished Professor at Bedford College in the University of London. But he was willing to have long conversations, and took me seriously. This was the beginning of fifty years of discussions, with David as mentor, and later as friend and colleague. David was ever willing to talk philosophy, anywhere – on trains, in museum cafes, and most memorably on the water, when he and I were sailing as crew on John McDowell's yacht in the stormy summer of 1973. David was undeterred in the conversational pursuit of philosophical issues, however choppy and perilous the seas were around us, as the vessel rocked.

Some of those discussions were about truth and meaning. David had visited Stanford in 1964 and 1965, and had had an early understanding of Donald Davidson's position on truth conditions and meaning. I had been impressed when attending Davidson's Locke Lectures in 1970. Davidson, I later learned, regarded David as an important expositor to Oxford philosophers of the conception that truth conditions are crucial in a philosophical account of meaning.Footnote ¹

That conception was implemented and folded into David's subsequent work on the right way of expounding the necessity of the identity relation, in effect a further exposition of the cluster of issues about objects and philosophical logic just noted. David held that the right way of expounding the necessity of identity has to treat ‘necessarily’ as sometimes a modifier of predicates, in particular as it occurs in the construction ‘is necessarily identical with’. If this position is to be developed in combination with a truth-condition conception of meaning, a truth-theoretic semantics with ‘necessarily’ treated as a predicate modifier must be provided. I learned more about the discipline and challenges in writing a truth theory in helping with the semantic clauses for that predicate modifier, and in helping with proofs in a corresponding truth theory, two years later.

I learned not only from the philosophical content of these discussions with David, I also took away a metaphilosophical and personal lesson. In addition to emotional empathy, there is such a thing as intellectual empathy, and it is its own virtue. Intellectual empathy is David's forte. It is a characteristic he shares with Montaigne, with whose humanity and general outlook he has a deep affinity.

Intellectual empathy can transform philosophical conversation and teaching. If you understand from the other's point of view their doubts, concerns, their philosophical hinterland, you will be able to communicate ideas in ways not otherwise available. This is part of what made David a superb tutor in the Oxford system of individual tutorials. I remember walking to the Oxford Examination Schools once with Simon Blackburn in the eighties in order to discover from the lists posted there how our students had fared in their final examinations. We were both impressed by how, once again, University College, of which David was then a Fellow, had received so many first class degrees. Intellectual empathy is essentially a matter of interpersonal relations. It is no wonder that David was, rightly, so alienated by the various teaching assessment exercises imposed on UK universities from the early nineties onwards. They took no account of this intellectual virtue, and promoted structures in which it could not flourish.

A second characteristic of David's philosophical thought that struck me from my first readings of his work is his integration of any specific topic with a wide-angle consideration of its location in relation to philosophical logic, to metaphysics, to epistemology, and to the theory of understanding.

In the case of philosophical logic and metaphysics, that is already clear in David's detailed discussion of the way in which the general role of sortals in identity plays out in the particular case of persons, and in various other kinds of entity. But this integration is present in other areas too, notably his moral philosophy. He worked more and more on this area after returning to Oxford in 1994 to take up the Wykeham Chair, and the topic arose in a B.Phil class that we gave jointly in the mid-nineties. David's position in moral philosophy has certain points of contact with Hume's views in moral philosophy, and, in the framework I offered in The Primacy of Metaphysics, it seems to me to be a no-priority position about moral properties and moral values. Under a no-priority position about the concepts of a given domain, neither the metaphysics of the properties picked out by the concepts nor the concepts of those properties are prior to the other in the order of philosophical explanation. They are irreducibly entangled, as a constitutive matter. David writes of moral values, ‘Such properties are to be conceived in the light of what it takes to exercise that grasp – not vice versa’ (2006, p. 334, David's italics). In another explicit formulation, he writes, ‘The objectivity of the reasonable exercise of the grasp of an ethical concept is not established by reference to the product of some independent understanding of the property. (Why should it need to be?) It is established by those who exercise it and engage fairly with first-order criticism’ (2006, p. 335).

The ‘vice versa’ positions with which he is drawing a contrast in the penultimate preceding quotation are positions that aim to individuate moral properties and values independently of human judgments about values. Those positions aim then to tie the grasp of moral concepts and values to an appropriate relation to the moral properties and values so individuated. David's position, close to but distinct from John McDowell's on these issues about moral understanding, was one of several factors that set me thinking about these issues more generally. As David notes, there are parallel issues about the relation between the metaphysics and theory of understanding for the domain of natural numbers. But the natural numbers, and our canonical concepts of them, form a domain in which a metaphysics-first view has more plausibility. So there are tensions here, of a fruitful kind that ought to impel further investigation. I mention this particular topic because it is one by which David's treatment, in situating his position in relation to vastly wider issues in metaphysics, epistemology, and the theory of understanding, brings us to the point of considering issues we might never have reached so promptly. Certainly his formulations have challenged me.

The third characteristic of David's thought is his ability always to frame his proposals as either further extensions, and sometimes as fruitful elaborations, of what we should preserve and recognize in the writings of great thinkers in the history of philosophy. Those philosophers are alive in his writings. The phenomenon is another illustration of David's intellectual empathy. The point could be made in connection with any one of Aristotle, or Hume, or Leibniz; but I will make it in connection with issues in theory of meaning and truth. Way back in 1971, in expounding a truth-conditional account of indicative sentence meaning, David noted that in the Grundgesetzse at I.32, Frege considered the conditions under which an expression ‘refers to the True’, and Frege then went on to state ‘The sense of this name, the thought, is: that these conditions are fulfilled’ (Wiggins, Reference Wiggins, Steinberg and Jakobovits1971, p. 17).Footnote ² Tracing such a truth-conditional account to Frege is illuminating in multiple ways, in addition to assigning credit correctly. Indeed, the significance of Frege's contribution goes beyond the bare statement just quoted. In a later essay, David writes of our need for a theory of such a kind that for each sentence of the relevant language, ‘the relevant axioms’ of the theory ‘deliver a theorem that determines a truth-condition for the sentence’. David continues, ‘In adapting Tarksi's general conception of formal theories of truth to this veritably Fregean end, Donald Davidson has filled an important lacuna in the Grundgesetze doctrine of sense’ (Wiggins, Reference Wiggins and van Straaten1980, p. 196). Davidson's contributions on this topic are secure, but on this matter Frege had already filled the suggested lacuna himself. Frege wrote, ‘For owing to our stipulations, it is determined under which conditions it [a correctly formed name – CP] refers to the True’ (also I.32). Frege is observing that his stipulations already provide a mini truth theory for his artificial language. Focusing on Frege, as David does, also avoids a potential historical injustice. For all his great contributions on truth theories, Tarski does not mention Frege's writing in ‘The Concept of Truth in Formalized Languages’, nor elsewhere in the essays of Logic, Semantics, Mathematics (Tarksi, Reference Tarski and Woodger1956). In tracing the truth-conditional conception of sense to Frege, David is also tracing its roots to the idea that the individuation of sense is inextricable from the fundamental conditions for something to be the reference of an expression.

In his essay ‘What Would be a Substantial Theory of Truth?’, David endorsed the thesis that a correct theory of truth for a language should, in combination with ‘a plausible anthropology’, make its speakers maximally intelligible to us. The thesis set me thinking for decades – not on the issue of whether it is true, for it is overwhelmingly plausible, but on the issue of how it could be true, of what made its truth possible. For any set of circumstances for a person, together with a proposed truth-theory for their language, and their actions, we seem to have the capacity to assess whether a certain set of propositional attitudes makes sense of the person and their actions. But this is an open-ended capacity in more than one respect. There are arbitrarily many such circumstances, and arbitrarily many sets of propositional attitudes, for which we have the capacity to assess whether the attribution makes our person intelligible. This open-ended capacity must have a finite basis. The basis must include the nature of the particular concepts expressed in the person's language, according to the candidate truth-theory. The fact that some combinations of candidate attitudes are unintelligible in certain circumstances sometimes traces back to the very nature of the concepts in the candidate attitudes. The attempt to explain the finite capacity by one or another treatment of concepts – by referentially-constrained conceptual role, or in more Fregean terms by a specific fundamental reference rule for the concept – has been with me since those early discussions with David. Whatever the correct answers, and however difficult, these questions seem philosophically basic; and as elsewhere, they are partly generated by previous advances in the discipline.

David's philosophy sets new questions in the many domains in which he has worked. For those of us fortunate to have enjoyed extended discussions with him, we are now, as philosophers, as we are partly because of the way his thought has developed – and partly because of his inimitable way of communicating it. In the same way that the great philosophers live in David's own writing, he lives in ours too.