The boundaries of psychology have never been very distinctly defined and, as a consequence, science has witnessed frequent border incidents. But it obviously is not psychology alone which suffers from such lack of delineation, but its neighbors, the biological and social sciences, do as well. Cooperation between sciences becomes difficult under these conditions. All agree that psychology is the science of mind, but few agree to what “mind” is. At least within our century “mind” has been taken to be “behavior”, (...) for the present day outlook is that mind is behavior rather than that which is responsible for behavior. The metaphysical dynamism of a prime mover has been replaced by an experimental concept, i.e., one that is susceptible to scientific investigation. There is no need to review the complex history of behavioristic psychology in its many ramifications, ranging from Watson's mechanism to the various vitalistic teleologies. We turn instead to a fundamental problem on which there is little agreement: “What kind of behavior should be called mind?”. (shrink)

Among the various meanings in which the word ‘probability’ is used in everyday language, in the discussion of scientists, and in the theories of probability, there are especially two which must be clearly distinguished. We shall use for them the terms ‘probability1’ and ‘probability2'. Probability1 is a logical concept, a certain logical relation between two sentences ; it is the same as the concept of degree of confirmation. I shall write briefly “c” for “degree of confirmation,” and “c” for “the (...) degree of confirmation of the hypothesis h on the evidence e“; the evidence is usually a report on the results of our observations. On the other hand, probability2 is an empirical concept; it is the relative frequency in the long run of one property with respect to another. The controversy between the so-called logical conception of probability, as represented e.g. by Keynes, and Jeffreys, and others, and the frequency conception, maintained e.g. by v. Mises and Reichenbach, seems to me futile. These two theories deal with two different probability concepts which are both of great importance for science. Therefore, the theories are not incompatible, but rather supplement each other. (shrink)

1. The problem. The concept of confirmation of an hypothesis by empirical evidence is of fundamental importance in the methodology of empirical science. For, first of all, a sentence cannot even be considered as expressing an empirical hypothesis at all unless it is theoretically capable of confirmation or disconfirmation, i.e. unless the kind of evidence can be characterized whose occurrence would confirm, or disconfirm, the sentence in question. And secondly, the acceptance or rejection of a sentence which does represent an (...) empirical hypothesis is determined, in scientific procedure, by the degree to which it is confirmed by relevant evidence. (shrink)