Okay, I think these are the two ideas the author is talking about:
- Human action is purposive behavior (Mises’ idea)
- Individuals have objectives and tend to choose the correct way to achieve them (David Friedman’s idea)
D. Friedman says of these two ideas that “the essential idea the same.”
Behaviour being purposive means simply that it aims at some end. But it being purposive doesn’t imply anything about whether that behaviour will in fact achieve that end or not, i.e, whether it’s correct or not, nor whether it’ll tend to be. I think Mises would have disagreed that individuals tend to choose the correct behaviour for their purposes. Mises criticised lots of ideas as failing to achieve their goals.
I think Mises’ idea means that all human action is goal directed and can explained in terms of goals/purposes.
D. Friedman’s idea doesn’t have such implications about how human action is explained. His idea is just that humans have objectives (which is compatible with some or most human action being non-purposive) and that they tend to choose correct ways to achieve those objectives (which isn’t implied by Mises’ idea and doesn’t imply Mises’ idea so it’s not the same idea.)
I don’t know if D. Friedman is misquoting Mises, but the actual first sentence of chapter 1 (from both my kindle version and physical version) of Human Action is (bold added):
Human action is purposeful behaviour.
So when D. Friedman says (bold added):
Rothbard starts with an axiom from Ludwig von Mises: Human action is purposive behavior, the first sentence of chapter 1 of his Human Action.
It seems misquote adjacent because he seems to go beyond paraphrasing when he identifies what he wrote as the first sentence of chapter 1 of Human Action, which is false.
Something that complicates this is that the book was initially released in German, not English, so there may be a English translated version that has the first sentence of chapter 1 using the word purposive?