This is our first and inevitable doubt, which requires solution. But it would be a quixotic proceeding first to make a void in our mind, and afterwards to admit into it, one by one, after investigation, such and such a concept, or such and such a principle. The illusion of the clean sweep and total reconstruction can never be too vigorously condemned. Is it from the void that we set out to think? Do we think in void, and with nothing? Common ideas of necessity form the groundwork for the broidery of our advanced thought. Further, even if we succeeded in our impossible task, should we, in so doing, have corrected the causes of error which are today graven upon the very structure of our intelligence, such as our past life has made it? These errors would not cease to act imperceptibly upon the work of revision intended to apply the remedy. It is from within, by an effort of immanent purgation, that the necessary reform must be brought about. And philosophy's first task is to institute critical reflection upon the obscure beginnings of thought, with a view to shedding light upon its spontaneous virgin condition, but without any vain claim to lift it out of the current in which it is actually plunged. One conclusion is already plain: the groundwork of common-sense is sure, but the form is suspicious. In common-sense is contained, at any rate virtually and in embryo, all that can ever be attained of reality, for reality is verification, not construction. Everything has its starting-point in construction and verification. Thus philosophical research can only be a conscious and deliberate return to the facts of primal intuition. But common-sense, being prepossessed in a practical direction, has doubtless subjected these facts to a process of interested alteration, which is artificial in proportion to the labour bestowed. Such is Mr Bergson's fundamental hypothesis, and it is far-reaching. "Many metaphysical difficulties probably arise from our habit of confounding speculation and practice; or of pushing an idea in the direction of utility, when we think we fathom it in theory; or, lastly, of employing in thought the forms of action." (Preface to "Matter and Memory". First edition.) The work of reform will consist therefore in freeing our intelligence from its utilitarian habits, by endeavouring at the outset to become clearly conscious of them.