Scientific men can handle these things-of-inference precisely as the blacksmith handles his tools. They are not thoughts as they are ordinarily used, not even in the logical sense of thought. They are rather things whose manipulation (as the blacksmith manipulates his tools) yield knowledge--or methods of knowledge--with a minimum of recourse to thinking and a maximum of efficiency. When one considers the importance of the enterprise of knowledge, it is not surprising that appropriate tools have been devised for carrying it on, and that these tools have no prototypes in pre-existent materials. They are real objects, but they are just the real objects which they are and not some other objects. THEORY AND PRACTICE Our last paragraphs have touched upon the nature of science. They contain, by way of intimation, an explanation of the distance which lies between the things of daily intercourse and the terms of science. Controlled inference is science, and science is, accordingly, a highly specialized industry. It is such a specialized mode of practice that it does not appear to be a mode of practice at all. This high specialization is part of the reason for the current antithesis of theory and practice, knowledge and conduct, the other part being the survival of the ancient conception of knowledge as intuitive and dialectical--the conception which is set forth in the Aristotelian logic. Starting from the hypothesis that the art of controlled inference requires for its efficient exercise specially adapted entities, it follows that the various sciences are the various forms which the industry of controlled inquiry assumes. It follows that the conceptions and formulations of the sciences--physical and mathematical--concern things which have been reshaped in view of the exigencies of regulated and fertile inference. To get things into the estate where such inference is practicable, many qualities of the water and air, cats and dogs, stones and stars, of daily intercourse with the world have been dropped or depressed. Much that was trivial or remote has been elevated and exaggerated. Neither the omissions nor the accentuations are arbitrary. They are purposeful. They represent the changes in the things of ordinary life which are needed to safeguard the important business of inference.