The present article attempts to investigate the 'philosophical foundations' of psychology and thereby of the social sciences in general with regard to a central problem, viz. the question of the 'inner'. It does this with special critical reference to an authoritative psychological theory, viz. the so-called 'mediation theory', and tries to show the necessity of interdisciplinary clarification. In the first part mediation theory was introduced as a variant of psychological behaviorism which attempts to substitute for the untenable total neglect of (...) 'inner' events a way of talking about them which is secured methodologically and retains a behavioral foundation. Of the three crucial questions raised by the project the second, viz. question, which concerns the theoretical status of the assumed inner mediators could be answered to the effect that they must be "hypothetical constructs" having the nature of real, phenomenally verifiable events, if, indeed, they are to figure as links in S-R-chains. Conceiving of them as "intervening variables", such a conception would exclude this function. The discussion of 'internalization' of behavior sequences as assumed by mediation theory has led to the conclusion that the relevant phenomena cannot, in this case, justify the necessity of a non-dispositional explanation which goes beyond 'external' performances ). Likewise the subject matter of question remained undecided; that is, the possibilities of phenomenally verifying the assumed 'inner' mediation processes which are only asserted to exist by the theory but are unspecified in content. Therefore, the observable performances in the case of sequential behaviour do not support the mediation theoretic solution of the problem of the 'inner'. (shrink)