With the development of empirical research, uncertainty or contingency is no longer regarded as infecting in a wholesale way an entire region, discrediting it save as it can be brought under the protecting aegis of universal truths as major premises. Uncertainty is now a matter of detail. It is the question whether the particular fact is really what it has been taken to be. It involves contrast, not of a fact as a fixed particular over against some fixed universal, but of the existing mode of apprehension with another possible better apprehension. From the standpoint of reasoning and proof the intellectual field is absolutely measured out in advance. Certainty is located in one part, intellectual indeterminateness or uncertainty in another. But when thinking becomes research, when the doubt-inquiry function comes to its own, the problem is just: What is the fact? Hence the extreme interest in details as such; in observing, collecting, and comparing particular causes, in analysis of structure down to its constituent elements, interest in atoms, cells, and in all matters of arrangement in space and time. The microscope, telescope, and spectroscope, the scalpel and microtome, the kymograph and the camera are not mere material appendages to thinking; they are as integral parts of investigative thought as were _Barbara_, _Celarent_, etc., of the logic of reasoning. Facts must be discovered, and to accomplish this, apparent "facts" must be resolved into their elements. Things must be readjusted in order to be held free from intrusion of impertinent circumstance and misleading suggestion. Instrumentalities of extending and rectifying research are, therefore, of themselves organs of thinking. The specialization of the sciences, the almost daily birth of a new science, is a logical necessity--not a mere historical episode. Every phase of experience must be investigated, and each characteristic aspect presents its own peculiar problems which demand, therefore, their own technique of investigation. The discovery of difficulties, the substitution of doubt for quiescent acceptance, are more important than the sanctioning of belief through proof. Hence the importance of noting apparent exceptions, negative instances, extreme cases, anomalies. The interest is in the discrepant because that stimulates inquiry, not in the fixed universal which would terminate it once for all. Hence the roaming over the earth and through the skies for new facts which may be incompatible with old theories, and which may suggest new points of view.