It's amazing how nonsensical the actual foundational axioms of modern day economics are.

Classical economics tried to tie economics to functions of physical things we can measure. Adam Smith for example proposed that because you can recursively decompose every product into the amount of physical units of time it takes to produce it all the way down the supply chain, then any stable economy should, on the average (not the individual case), roughly buy and sell in a way that reflects that time, or else there would necessarily have to be physical time shortages or waste which would lead to economic problems. We thus may be able to use this time parameter to make quantifiable predictions about the economy.

Many people had philosophical objections to this because it violates free will. If you can predict roughly what society will do based on physicals factors, then you are implying that people's decisions are determined by physical parameters. Humans have the "free will" to just choose to buy and sell at whatever price they want, and so the economy cannot be reduced beyond the decisions of the human spirit. There was thus a second school of economics which tried to argue that maybe you could derive prices from measuring how much people subjectively desire things, measured in "utils."

"Utils" are of course such ambiguous nonsense that eventually these economists realized that this cannot work, so they proposed a different idea instead, which is to focus on marginal rates of substitution. Rather than saying there is some quantifiable parameter of "utils," you say that every person would be willing to trade some quantity of object X for some quantity of object Y, and then you try to define the whole economy in terms of these substitutions.

However, there are two obvious problems with this.

The first problem is that to know how people would be willing to substitute things rigorously, you would need an incredibly deep and complex understanding of human psychology, which the founders of neoclassical economics did not have. Without a rigorous definition, you could not fit it to mathematical equations. It would just be vague philosophy.

How did they solve this? They... made it up. I am not kidding you. Look up the axioms for consumer preference theory whenever you have the chance. It is a bunch of made up axioms about human psychology, many of which are quite obviously not even correct (such as, you have to assume that the person has evaluated and rated every product in the entire economy, you have to assume that every person would be more satisfied with having more of any given object, etc), but you have to adopt those axioms in order to derive any of the mathematics at all.

The second problem is one first pointed out, to my knowledge, by the economist Nikolai Bukharin, which is that an economic model based around human psychology cannot possibly even be predictive because there is no logical reason to believe that the behavior of everything in the economy, including all social structures, is purely derivative of human psychology, i.e. that you cannot have a back-reaction whereby preexisting social structures and environmental factors people are born into shape their psychology, and he gives a good proof-by-contradiction that the back-reaction must exist.

The idea that you can derive everything based upon some arbitrary set of immutable mathematical laws made up in someone's armchair one day that supposedly rigorously details human behavior that is irreducible beyond anything else is just nonsense. No one has ever even tested any of these laws that supposedly govern human psychology.