Viz. his original error about how Mises conceived economics. I have transcribed the specific quote I am referring to:
“I made the mistake. I thought Mises said the truth of economics is synthetic a priori truth. What do we mean by synthetic? Well synthetic a priori truth would be one that is a priori. We can know its true just by thinking about it. It would not be one we could just discover to be true just by looking at the implications of the concept. It would be one that’s true about the world but not one that’s just true from the nature of the concept. So at one time I thought ‘Mises said the truth of economics are synthetic a priori, but in fact he doesn’t say that in Human Action. He says they’re tautologies, which would be that they’re not synthetic a priori truth. Whether he’s right to hold that view is another question, but that was his view.”
Looking at Free Advice consultingbyrpm.com/blog, there are so many who hold this position. This comes from a lack of understanding about basic philosophical concepts. One of the main epiphanies I originally came to was from a very old book called Physical Realism by Thomas Case. This book outlines a critique on modern philosophy in its entirety, especially on the errors of the Kantian system. Traditional logicians used the terms analytic and a priori for the exact same things, likewise for synthetic and a posteriori.
Note that the author in this paper agrees about this confusion about synthetic and analytic distinctions:
Now I have linked to this paper before, but I would like to highlight his section on synthetic and analytic distinctions.
Moreover, this is not the only praxeologist who has critiqued Hoppe and Rothbard:
Knot thinks Hoppe is grossly confused about the a priori, not to mention his and Rothbard’s ethical systems.
So, I think the Austrian community could use a clarification on this, even though this will probably go unheard.