THE NEW LOGIC.--But it was not only the scientific dogmas of the old system that had been so rudely overthrown--the very principles upon which those dogmas rested had been submitted to a destructive criticism. The new science produced a new logic. This order of events is not unusual: first, the new scientific discoveries, and then in the wake of the discoverers, comes the innovating critic who systematises the logical or scientific methods to which the new knowledge seems to have been due. First, Kepler and Galileo, who used the "inductive" method, and then Lord Bacon of Verulam (1561-1626), who discovered the inductive logic, and established it as a system. FRANCIS BACON.--Bacon's doctrine may be summarised by his own epigram, "If a man begin with certainties, he shall end in doubts; but if he be content to begin with doubts, he shall end in certainties." Which is really a criticism of what is known as the a priori method, whereby the inquirer starts with certain predefined theories to which all phenomena must conform, and which all experience must verify. If facts will not suit the particular theory, so much the worse for the facts: one could always disregard them, and apply a blind eye to Galileo's telescope. Such is always the procedure of the dogmatic mind, which is already so certain of the truth of its notions that no evidence can persuade it to the contrary. But it is not by such means that knowledge is advanced, and it was for a reversal of these that Bacon pleaded. Leonardo da Vinci had already anticipated the Baconian logic (which did not wait for Bacon until it was applied) when he laid down the proposition that wisdom was the daughter of experience, and rejected all speculations which experience, the common mother of all sciences, could not confirm. Hence, knowledge was the product of time; the process of collecting material for a judgment must often be slow, but the results were worth the labour--these would not be speculative, but true. Nor need it be supposed that Bacon excluded imagination from playing a part in increasing knowledge, he did not plead _only_ for a mechanical collection of material. It is imagination which in face of abundant material creates the hypothesis which accounts for it being what it is. And he was prepared to admit the value of preliminary hypotheses which might be replaced as further facts were collected, or as insight became more clear. Here, too, Bacon describes the method followed by modern science.