My only regret is that I have but one downvote to give for this sub.

The idea of praxeology was interesting from a historical perspective. As logical positivism was being developed, Max Weber (and other social theorists) observed that the principles of positivism were not useful for the social sciences. The notion of verifiable "first principles" could not be applied to human behavior -- even a loose interpretation of "free will" would immediately discredit the primary status of any such axiom. Mises, whose brother was a member of the Vienna circle, was acutely aware of this problem. He therefore sought to lay the foundation for an alternative epistemology that was applicable to the social realm.

Mises's idea followed from basic propositional logic: Any conclusion deduced from a true proposition must be true:

p	q	p -> q
T	T	T
F	T	T
T	F	F
F	F	T

All that was needed was a true premise. But this, of course, was problematic -- Hume's classic problem of induction seems to ensure that no empirical result can ever be confirmed as unambiguously true.

Mises's solution to this problem lay in the Kantian idea of the synthetic. In his Critique of Pure Reason, Kant distinguished the idea of a priori/a posteriori from the idea of analytic/synthetic. Propositions can be true a priori despite the fact that the conclusion is not contained in the predicate; the existence of the number "4" is not implied by the existence of the number "2", yet the statement "2+2=4" remains a priori true. All that was left, then, was to find a suitable synthetic prior that could be utilized to deduce social science. This prior, of course, is what is now infamously known as the "action axiom":

Human action is purposeful behavior. Or we may say: Action is will put into operation and transformed into an agency, is aiming at ends and goals, is the ego's meaningful response to stimuli and to the conditions of its environment, is a person's conscious adjustment to the state of the universe that determines his life. Such paraphrases may clarify the definition given and prevent possible misinterpretations. But the definition itself is adequate and does not need complement of commentary (Mises, Human Action).

But here is where we go off the rails. First, note how Mises presupposes the existence of agency -- the idea that "conscious" choices can be distinguished from the unconscious. This premise can be criticized a priori in a manner similar to Kierkegaard's critique of Descartes's cogito -- "free will" is contained in the predicate, yet does not exist a priori. This premise has also been shown to be false empirically. Through the work of Kahneman and Tversky (and countless other experimental psychologists), we now know that agency does not exist in any manor befitting of a synthetic antecedent.

But this is not the most serious problem facing praxeology. Look again at the previous truth table, this time focusing on the third row:

p	q	p -> q
T	T	T
F	T	T
T	F	F
F	F	T

The truth of the premise alone is not sufficient to ensure the truth of the conclusion -- we also need the deductive statement "p -> q" to hold true as well. This is the death knell -- any inaccuracy in the deductive methodology invalidates the results of the theory. The potential for this problem is amplified by the rejection of formal mathematics. The ambiguity of linguistics and semantics is an affront to Wittgenstein's famous edict -- The 600 pages of Mises's Human Action have no simplistic authority.

Contemporary followers of Mises revel in the semantic ambiguity. "The theory cannot be falsified," they exclaim, "because we reject empiricism. The true premise ensures that our conclusions must be true, regardless of any observed phenomenon." But this argument betrays the entire logical foundation of praxeology. The initial appeal to propositional logic becomes their petard, for the observation ¬q necessarily implies that either the deduction or the axiom is false. Neither the truth of the axiom nor the deduction is sufficient to ensure the truth of q. The statement "I reject empiricism" itself contradicts the very foundations of praxeology -- the conclusion q must be true a posteriori in order for p to exist a priori.

And so we reach the rhetorical position of modern Austrians. Faced with this reality, they simply refuse to acknowledge that either their deductive process or their axiom is false, for in so doing they would invalidate the entire enterprise. Instead they simply accuse critics of not understanding the "true" nature of praxeology or retreat to a circularly defined epistemology. In this regard the modern praxeologist isn't just wrong, but is also anti-intellectual.

TL;DR: "derp! Austrians is so dumb! They don't even science bro!"