Nigel Warburton & Sophie Roell in Five Books:
The history of philosophy is obviously long, and different people will view it different ways. Do you have an overarching view about the history of philosophy?
Justin E. H. Smith: I am a historian of philosophy who takes seriously the categories of the people whom I study. That is, I try to understand philosophy the way they understood it, rather than the way we understand it. In particular, this means I take seriously the notion that until sometime in the 18th century—maybe even into the 19th century—there was a category that no longer exists called ‘natural philosophy’, which was supplanted by the category of science over the course of the 19th century.
Until then, it was simply taken for granted that what we now think of as scientific inquiry was part of philosophy. That’s why you have these strange vestiges of that period. For example, The Philosophical Transactions of the Royal Society still exists today as a science journal. That’s because when it was founded in the 1660s, it made perfect sense to call studies on spontaneous generation or on the formation of clouds ‘philosophy’.
I contend that the books I propose to discuss are books on the history of philosophy because I take actors’ categories seriously. I believe that figures who belong to the history of science prior to sometime in the 18th century were certain kinds of philosophers. In many cases—as with, say, Aristotle, Descartes, Leibniz—they were philosophers in our narrower, restricted sense, and they were also natural philosophers.
More here.