Answer:
To say that a man acts with a purpose, we are implying that the man believes his action will achieve the result he desires. (If we didn't attribute such a belief to the man, then our description would make no sense.) This seems like a trivial point, but much of the development of economics in the twentieth century involved the growing realization among economists that expectations were important. These developments lie outside the scope of this course, but the moral is that these "foundational" issues really do have implications for cutting edge research.