There is no such thing as water in general, but water is just this water, at this time, in this place, and it never shows itself twice, never recurs. The scientist must deal, therefore, with particular historic cases of water, and with their specific origins. "Experiment has to do with the conditions of production of a specific amount of water, at a specific time and place, under specific circumstances: in a word, it must deal with just _this_ water. The conditions which define its origin must be stated with equal definiteness and circumstantiality."[151] The instance has as definite a place in an historical series as has Julius Caesar. But the difference in treatment of the water and Caesar is due to the difference in interest. "Julius Caesar served a purpose which no other individual, at any other time, could have served. There is a peculiar flavor of human meaning and accomplishment about him which has no substitute or equivalent. Not so with water. While each portion is absolutely unique in its occurrence, yet one lot will serve our intellectual or practical needs just as well as any other."[152] For this reason the specific case of water is not dealt with on its own account, but only as giving insight into the processes of its generation in general. In this way the difference arises between the generalized statements of physical science and the individualized form demanded in historical science. The abstract character of the physical result is recognized by the hypothetical form of judgment in modern logic; if certain conditions, then certain consequences. But the counterpart of this must not be forgotten, that every categorical proposition applies to an individual. Experimental propositions, therefore, have an historical value. "They take their rise in, and they find their application to, a world of unique and changing things: an evolutionary universe."[153] The recognition of the historical character of experimental science does not in any way derogate from its value, but, properly understood, gives a deeper insight into its significance. It should be observed that here also Dewey treats thought, hypothesis, as coming 'after something, and for the sake of something.'