Yet there is a valid distinction between knowledge which is objective and impersonal, and thinking which is subjective and personal. In one sense, knowledge is that which we take for granted. It is that which is settled, disposed of, established, under control. What we fully know, we do not need to think about. In common phrase, it is certain, assured. And this does not mean a mere feeling of certainty. It denotes not a sentiment, but a practical attitude, a readiness to act without reserve or quibble. Of course we may be mistaken. What is taken for knowledge--for fact and truth--at a given time may not be such. But everything which is assumed without question, which is taken for granted in our intercourse with one another and nature is what, at the given time, is called knowledge. Thinking on the contrary, starts, as we have seen, from doubt or uncertainty. It marks an inquiring, hunting, searching attitude, instead of one of mastery and possession. Through its critical process true knowledge is revised and extended, and our convictions as to the state of things reorganized. Clearly the last few centuries have been typically a period of revision and reorganization of beliefs. Men did not really throw away all transmitted beliefs concerning the realities of existence, and start afresh upon the basis of their private, exclusive sensations and ideas. They could not have done so if they had wished to, and if it had been possible general imbecility would have been the only outcome. Men set out from what had passed as knowledge, and critically investigated the grounds upon which it rested; they noted exceptions; they used new mechanical appliances to bring to light data inconsistent with what had been believed; they used their imaginations to conceive a world different from that in which their forefathers had put their trust. The work was a piecemeal, a retail, business. One problem was tackled at a time. The net results of all the revisions amounted, however, to a revolution of prior conceptions of the world. What occurred was a reorganization of prior intellectual habitudes, infinitely more efficient than a cutting loose from all connections would have been.