1. Some Preliminary Distinctions. The relation between the natural and the social sciences, as it bears on their respective subject-matters, methods, and propositions, has long been a source of problems for the philosophy of science. The title of this paper is intended to indicate one of the most basic of these problems. Before developing my point, however, I wish to guard against a possible misinterpretation. I am not questioning the accepted fact that as knowledge in any field advances men may come to recognize the incorrectness of what they had previously regarded as “laws” in that field, and may consequently “change” these laws to take account of such increased knowledge. Let me call this kind of change of laws doctrinal change. The kind of change about which I am asking is rather a change in the subject-matter itself insofar as it is subject to laws—i.e., a change in the causal relations among the facts, objects, properties, events, or whatever they may be called, with which the science deals. Let me call this kind of change of laws factual change. Now, without inquiring more fully at the moment into the nature of scientific laws as such, we may say that the history of science shows that men can and do effect doctrinal changes in the laws of any science, natural as well as social, and formal as well as empirical. And it is recognized also, with minor exceptions to be noted later, that men cannot effect factual changes in the laws of the natural sciences, since these are independent of human volition or decision. The question I am asking, then, is whether men can effect factual changes in the laws of the social sciences.