Nor can verification, indubitable proof, be demanded and furnished as it can in many parts of the field cultivated by the special sciences.  We may judge science fairly well without ourselves being scientists, but it is not possible to judge philosophy without being to some extent a philosopher.

In other words, the conclusions of reflective thought must be judged by following the process and discovering its cogency or the reverse.  Thus, when the philosopher lays before us an argument to prove that we must regard the only ultimate reality in the world as unknowable, and must abandon our theistic convictions, how shall we make a decision as to whether he is right or is wrong?  May we expect that the day will come when he will be justified or condemned as is the astronomer on the day predicted for an eclipse?  Neither the philosophy of Locke, nor that of Descartes, nor that of Kant, can be vindicated as can a prediction touching an eclipse of the sun.  To judge these men, we must learn to think with them, to survey the road by which they travel; and this we cannot do until we have learned the art.

Whether we like to admit it or not, we must admit, if we are fair-minded and intelligent, that philosophy cannot speak with the same authority as science, where science has been able to verify its results.  There are, of course, scientific hypotheses and speculations which should be regarded as being quite as uncertain as anything brought forward by the philosophers.  But, admitting this, the fact remains that there is a difference between the two fields as a whole, and that the philosopher should learn not to speak with an assumption of authority.  No final philosophy has been attained, so palpably firm in its foundation, and so admittedly trustworthy in its construction, that we are justified in saying:  Now we need never go back to the past unless to gratify the historic interest.  It is a weakness of young men, and of older men of partisan temper, to feel very sure of matters which, in the nature of things, must remain uncertain.

Since these things are so, and since men possess the power of reflection in very varying degree, it is not surprising that we find it worth while to turn back and study the thoughts of those who have had a genius for reflection, even though they lived at a time when modern science was awaiting its birth.  Some things cannot be known until other things are known; often there must be a vast collection of individual facts before the generalizations of science can come into being.  But many of the problems with which reflective thought is still struggling have not been furthered in the least by information which has been collected during the centuries which have elapsed since they were attacked by the early Greek philosophers.