[T]here is a sense in which the word rationality can be used which renders it legitimate to argue that at least some rationality is assumed before human behaviour has an economic aspect – the sense, namely, in which it is equivalent to “purposive”.… [I]t is arguable that if behaviour is not conceived of as purposive, then the conception of the means-end relationships which economics studies has no meaning. So if there were no purposive action, it could be argued that there were no economic phenomena. But to say this is not to say in the least that all purposive action is completely consistent. It may indeed be urged that the more that purposive action becomes conscious of itself, the more it necessarily becomes consistent. But this is not to say that it is necessary to assume ab initio that it always is consistent or that the economic generalizations are limited to that, perhaps, tiny section of conduct where all inconsistencies have been resolved.