For this blog, I will write about topics for 20 minutes and that is all.
Many people think about the law of marginal of utility and think about value scales. Well, value scales don’t exist, unless you are talking about a value scale in a very abstract sense.
I believe Rothbard, among many other Austrians, are very confused about this. If you are going to read this blog, you will get used to the fact that I probably not going to look up many of the things that I make reference to. Maybe I will later if people want, but many people may not read this blog.
Back to marginal utility. Whenever Mises talks about any economic laws, they are only in reference to actual actions that take place. So, when a person is thinking of a value scale, this is an action IN ITSELF. Therefore, value scales can’t be inherent in making actions. When I perform any action, I don’t choose this action among a list of actions that I may have partaken in. Instead, the law of marginal utility is a proposition (analytic a priori) that is inherent in actions themselves. Performing an action is tautologous to valuing something. I would like to give credit to Adam Knott (praxeology.org) on this, but I still think his formulation is in error, which I must reserve for another post.
For those who may be confused, praxeology makes no synthetic propositions. Praxeology takes action as given. It does not analyze the metaphysical grounds for accepting the action axiom. It merely analyzes the axiom and accepts its truth.
So, we now have the proposition: Performing an action is valuing something. Surely, I can right now perform an action that I don’t value, thereby disproving your proposition. Well my 20 minutes is up, so I should answer this objection in my next post.
hanktheblog 
I would like to post MF’s reply so that I may respond to it in the future, since he did not comment here himself.
Major_Freedom
OK, I’ve read it. In a word, I think it’s incorrect.
The law of marginal utility is synthetic a priori, because it is referring to not just a law of thought, but a law of action in the real world.
If you understand the laws of thought to be actions, you’ll then know that the laws of thought are necessary truths about the laws of the “external” world constrained to actions.
I would argue that the law of marginal utility not synthetic a priori, at least according to Mises. To Mises, all economic propositions are analytic a priori propositions. Only if Major_Freedom disagrees with me will I look up sources to back up my claim.
It is analytic because it is derived analytically from the action axiom. The status of the action axiom I don’t really wish to engage in.