But the perfect work of art or love, when done, becomes not merely the canon by which to test progress; it becomes itself the cause of progress, both because of its more perfect revelation of the ideal and because of the emulation which it arouses in others to go and do likewise. They likewise strive after the ideal and labour for its sake: it is the final cause of their endeavours, the purpose of their attempts; and were there no such final cause there would be no progress. The ideal is a principle both of thought and action, the test of knowledge and the source of progress. Truth is the ideal of science: approximation to truth is that for which the man of science labours and that in which he conceives that scientific progress lies. The gravitation formula not only expresses a wide-reaching truth, but has acted as an incentive to many attempts to extend it to the domain of chemistry, and serves as an ideal yet to be rivalled in other branches of science. But science and progress in science are alike impossible, if consciousness and experience be discredited, or if the ideal of science be not real, _i.e._ if the laws of science have not the permanence, the independence, and the self-identity which are the attributes of the real, but are as transient as the minds that discovered them, exist only when thought of by man, and are not really the same at different times. But if these ideals, whether of truth, beauty, or goodness, are thus real, then they are "our" ideals only in the sense that we are aware of them and adopt them, not in the sense that we make them; they are ours because they are present in the common consciousness of mankind, but not in the sense that they are created by that consciousness. They are revealed to man before they are manifested by man.