I can't shake the feeling that it's presumptuous to be up here speaking about David Lewis, whose life and work spoke so clearly for themselves. But we're here to remember, and to pay tribute, so please forgive me in advance for presuming.
What was David's philosophical essence? David would have rejected the question, of course. But he would have allowed us to ask about important respects of comparison to counterparts; so we can at least look at strands in his work that locate him in philosophical space.
In looking over David's whole body of work, I'm struck especially by the following. David started his career looking for all the world like an empiricist in the tradition of Hume and Carnap; by the end of his career, it was clear that he was the great rationalist of twentieth century philosophy. Interestingly, it doesn't seem that he changed his mind in any major way. Rather, these strands coexist seamlessly. How could this be? If you look at David's two most salient counterparts in the history of philosophy, it looks like a bad joke: What do you get when you cross David Hume with Gottfried Leibnitz? Not Gottfried Heim; David Lewitz. The miracle of David's career is that he somehow made this make sense.
In retrospect it's clear how this worked. David was the sort of empiricist who starts at the surface, but allows carefully constrained steps beyond it in the search for explanation. And he applied this method of constrained abduction not just to the deliverances of perception, but to the surface structure of thought. It's striking that the first half of David's career was dominated by the philosophy of language and mind, while the second half was dominated by metaphysics. For the most part, David's philosophy of language and mind was resolutely empiricist; it wouldn't have seemed out of place in Carnap. But along the way, David's empiricist systematization of these phenomena made unreduced appeal to notions that David took to call out for explanation themselves: properties, causation, mathematics, and of course possibility and necessity, again and again. Here the quest for explanation and the taste for simplicity took over.
In these domains, David saw unity and regularity that called out for explanation in simpler terms. But as elsewhere, simplicity required going beyond the surface: in some cases, famously, well beyond. But these moves were always heavily constrained, by weighing costs and benefits. Sometimes the ontological costs seemed pretty low, as when he reduced causation to modality, or mathematics to mereology, plus or minus a bit. In other cases it was higher: the space of worlds, perfectly natural classes. There was plenty of room for disagreement, but David thought that the remarkable explanatory benefits always justified the ontological costs. The result was a beautiful simple system: a fundamental physics for philosophy, one might say.
Ultimately, I think we can see David as a scientist of the a priori, and his career as one long inference to the best explanation. Of course David wasn't the first philosopher to take this approach, but he gave it perhaps its purest and most powerful form. In a century dominated by empiricism, it's easy to see his work as rehabilitating a sort of rationalism, with his a priori starting points, his systematic method, and the boldness of his inferences. But at the same time, the convergence of empiricist and rationalist strands in his work did much to make the division seem inessential. One can discern a similar convergence in much analytic philosophy at the start of the twenty-first century. Many people have contributed to this change of climate, but a significant part of it has been due to David's showing the way.
David wasn't just an extraordinary philosopher, of course; he was an extraordinary person. I didn't know him as long or as well as many people here did, but he certainly left an impression. I first encountered him as a graduate student. He had read something of mine — it was a job application, not very well-put-together — and he was calling out of the blue with advice: this is what you're doing wrong, this is what you could do better. This sort of thing was absolutely typical of David's generosity and support, particularly toward young philosophers. And particularly toward Australians, too. For a young Australian philosopher, David's support was just about inevitable. To me, and to many others, it made all the difference.
I eventually met David, here in Princeton. My first reaction was pretty typical, I imagine: I was completely terrified, for about fifteen minutes. I can remember asking a question, and getting no response for at least a minute. I figured "OK, he doesn't answer a question unless he thinks it's worth answering", and asked him another. (It was only later that someone told me "Slow down — he always answers eventually".) But pretty quickly, David's shy warmth would show through his silences, especially with Steffi around to make everyone feel at home.
Like many others, I knew David best through correspondence: no e-mail, so instead a stream of letters and faxes, always on the same old printer. David did so much philosophy this way that I hope one day someone publishes a collection of his correspondence: maybe some of it could be set in that same typeface, which is the way I always imagine David's philosophical work. Just a couple of hours before I heard of David's death, I had been into the department to see if there was a fax from David: I had sent him a paper, and was keen to hear what he thought. Now of course I'll never know.
For me, and I think for many of us, David's clarity, insight, and integrity made him a sort of philosophical touchstone: he was a measure of what was good in philosophy, and he was a symbol of what was good about philosophy. Now our touchstone is gone, and we can't help feeling a bit adrift. David didn't believe in touchstones, of course: just in the Humean mosaic of our natural world, and in the space of worlds to which ours belongs. We can console ourselves with the Humean touchstone he left us with: deep patterns and regularities throughout our lives, and throughout our local slice of philosophical space. All of us are richer for it.
Photos from the weekend of the memorial service,
Others' remarks at the memorial service