When does philosophy cease to be philosophy?

In The Problems of Philosophy Bertrand Russell writes:

Philosophy, like all other studies, aims primarily at knowledge. The knowledge it aims at is the kind of knowledge which gives unity and system to the body of the sciences, and the kind which results from a critical examination of the grounds of our convictions, prejudices, and beliefs. But it cannot be maintained that philosophy has had any very great measure of success in its attempts to provide definite answers to its questions. If you ask a mathematician, a mineralogist, a historian, or any other man of learning, what definite body of truths has been ascertained by his science, his answer will last as long as you are willing to listen. But if you put the same question to a philosopher, he will, if he is candid, have to confess that his study has not achieved positive results such as have been achieved by other sciences. It is true that this is partly accounted for by the fact that, as soon as definite knowledge concerning any subject becomes possible, this subject ceases to be called philosophy, and becomes a separate science. The whole study of the heavens, which now belongs to astronomy, was once included in philosophy; Newton’s great work was called ‘the mathematical principles of natural philosophy’. Similarly, the study of the human mind, which was a part of philosophy, has now been separated from philosophy and has become the science of psychology. Thus, to a great extent, the uncertainty of philosophy is more apparent than real: those questions which are already capable of definite answers are placed in the sciences, while those only to which, at present, no definite answer can be given, remain to form the residue which is called philosophy.

Russell wrote this in 1912, but his theory remains poplar to this day, especially in philosophy circles. It’s not hard to guess what makes it attractive. But can it really let philosophers off the hook in the face of the “no progress” accusation? I’m no historian of ideas, but my encounters with 200+ year old material labelled “philosophy” suggest that Russell is simply wrong.

Take the 1664 Experimental Philosophy, In Three Books: Containing New Experiments Microscopical, Mercurial, Magnetical. By Henry Power, Dr. of Physick. The content is mostly what we’d today call biology, physics and engineering, with occasional hints of philosophy. Power contrasts his own empirically-oriented philosophy, which is “magnificent”, with the philosophy of “Peripateticks, Dogmatists and Notional Speculators”, which is “Rubbish”:

This is the Age wherein (me-thinks) Philosophy comes in with a Spring-tide; and the Peripateticks may as well hope to stop the Current of the Tide, or (with Xerxes) to fetter the Ocean, as hinder the overflowing of free Philosophy: Me-thinks, I see how all the old Rubbish must be thrown away, and the rotten Buildings be overthrown, and carried away with so powerful an Inundation. These are the days that must lay a new Foundation of a more magnificent Philosophy, never to be overthrown: that will Empirically and Sensibly canvass the Phenomena of Nature, deducing the causes of things from such Originals in Nature, as we observe are producible by Art, and the infallible demonstration of Mechanicks: and certainly, this is the way, and no other, to build a true and permanent Philosophy.

The questions Power asks in the book are mostly quite straightforward and “capable of definite answers”, both today and in Power’s time, like:

• “Do insects have a heart and how do we find out?”
• “What is the role of the nerves in facilitating motion?”
• “What kinds of coal mine damps are there?”
• “What is the relation between colour and light?”
• “How do eyes work?”
• “Does the Earth move?”
• “Does vacuum exist?”
• “Is human hair hollow and if not, how come do people in Poland bleed from their hair?”

Today we’d call them “empirical” or “scientific”, but in the 17^th century and long afterwards, they were called “philosophical”. So it’s simply not the case that we stopped calling them “philosophical” as we learnt how to go about answering them. Surely our answers to these questions today are much more accurate than Power’s – but I don’t think this is what Russell had in mind when he wrote about “the possibility of definite knowledge”. Rather, it seems that the concept of philosophy has changed over time.

This of course doesn’t mean that philosophy (as we understand it today) doesn’t make any progress. It doesn’t even mean that philosophy never hands problems over to science in some way. It does, however, mean that the popular account of the historical interaction between science and philosophy is most likely mistaken.