On the other hand, a science which sincerely desires to progress needs fixed foundations as little as fixed ideas, and firm ground as little as assurances to ‘rest’ on. It needs only a starting-point, or jumping-off place, whence it can plunge into the unharvested seas of the unknown. Now the essence of a starting-point is to be a place you want to get away from, and its excellence lies in being such as to prompt you to leave it as easily and eagerly as possible. If, therefore, scientific ‘principles’ (ἀρχαί) are really to be starting-points, they need not, and must not, be so comfortable and so deceptively similar to ‘absolute’ truths as to tempt the scientific spirit to repose. They should be tentative assumptions which are gladly abandoned in the hope of reaching something better, stepping-stones to farther and higher things, which are valued for their consequences, and logically dependent on the conclusions to which they formed the premisses. The logic of science, therefore, has no reason to postulate stability or solidity for its initial principles: the most indispensable of them are only principles of method, and even of the tried and tested principles it arrives at the ‘validity’ (= strength) demanded is merely that they should be able to float the accumulated wealth of knowledge down the stream of time. IV § 30. It is clear, then, that the time has come when Science should break decisively with the logical tradition, and proclaim a logic of its own which has always been implicit in its procedure. It must definitely declare that what it needs is not a logic which describes only the static relations of an unchanging system of knowledge, but one which is open to perceive motion, and willing to appreciate the dynamic process of a knowledge that never ceases to grow, and is never really stereotyped into a system. To show that such a logic is not inconceivable will be the endeavour of the concluding sections of this essay. We have already had occasion to note many of the most important features of this logic. We have seen that logical, i.e. critical, reflection upon discovery must start from, and be guided by, the conception of a scientific _problem_ with which the process of knowing _experiments_ (§ 21). This problem has, of course, to be attacked with the existing resources of a science, i.e. with the knowledge it possesses up to date. These resources form the scientific _capital_ which is necessarily _risked_ in research if it is to yield interest. It comprises (_a_) approved principles, (_b_) known facts, and (_c_) established meanings of words. About each of them a little more may advantageously be said.