The methods of science by which the revolution in our knowledge of the world dating from the seventeenth century, was brought about, teach the same lesson. For these methods are nothing but experimentation carried out under conditions of deliberate control. To the Greek, it seemed absurd that such an activity as, say, the cobbler punching holes in leather, or using wax and needle and thread, could give an adequate knowledge of the world. It seemed almost axiomatic that for true knowledge we must have recourse to concepts coming from a reason above experience. But the introduction of the experimental method signified precisely that such operations, carried on under conditions of control, are just the ways in which fruitful ideas about nature are obtained and tested. In other words, it is only needed to conduct such an operation as the pouring of an acid on a metal for the purpose of getting knowledge instead of for the purpose of getting a trade result, in order to lay hold of the principle upon which the science of nature was henceforth to depend. Sense perceptions were indeed indispensable, but there was less reliance upon sense perceptions in their natural or customary form than in the older science. They were no longer regarded as containing within themselves some 'form' or 'species' of universal kind in a disguised mask of sense which could be stripped off by rational thought. On the contrary, the first thing was to alter and extend the data of sense perception: to act upon the given objects of sense by the lens of the telescope and microscope, and by all sorts of experimental devices. To accomplish this in a way which would arouse new ideas (hypotheses, theories) required even more general ideas (like those of mathematics) than were at the command of ancient science. But these general conceptions were no longer taken to give knowledge in themselves. They were implements for instituting, conducting, interpreting experimental inquiries and formulating their results.