Most of my publications over many years have in one way or another been about, or concerned with, natural philosophy. In all those years, however, neither I nor anyone else has seen fit to write a history of that discipline. Although numerous histories of science have been published, and will undoubtedly continue to appear, I am unaware of any history of natural philosophy. It occurred to me that an account of the historical evolution of natural philosophy should prove helpful to a better understanding of the development of the history of science itself. Indeed, as readers will discover, the historical relationship between natural philosophy and science is by no means straightforward. Opinions about their association and interconnections have often been controversial and sometimes quite elusive.

Once I determined to write a history of natural philosophy, I had to decide whether that history should be all encompassing – from its origins to its general replacement by modern science – or whether it should be confined to one or two historical periods. Because my area of specialization has been the late Middle Ages, it seemed plausible to begin with the origins of natural philosophy in the ancient world and conclude at about 1500, when medieval natural philosophy reached the height of its development. Around 1998 I became aware of an opinion that claimed that natural philosophy was always about God, even when God is not discussed or mentioned; and, consequently, that natural philosophy could not be science, because the latter was never about God.