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…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.
I often hear this selection effect explanation for the apparently small number of resolved problems that philosophy can boast. I don’t think it necessarily lessens this criticism of philosophy however. It matters whether the methods that were successful at providing insights in what were to become fields like psychology and astronomy – those which brought definite answers within reach – were methods presently included in philosophy. If they were not, then the fact that the word ‘philosophy’ has come to apply to a smaller set of methods which haven’t been successful does not particularly suggest that such methods will become successful in that way*. If they were the same methods, then that is more promising.
I don’t know which of these is the case. I also don’t actually know how many resolved problems philosophy has. If you do, feel free to tell me. I start a PhD in philosophy in the Autumn, and haven’t officially studied it before, so I am curious about its merits.
*Note that collecting resolved problems is only one way philosophy might be valuable. Russell points out that philosophy has been productive at making us less certain about things we thought we knew, which is important information.