> As everything in economics, it depends on which branch you're talking about, but this assumption is the core of the marginalist revolution which is fundamental to the whole classical branch and it's derivatives
Marginalism is saying something much more precise than that. It is saying that (in the given example) the two people value their marginal dollars differently than they value one marginal unit of coffee. A statement which is certainly objectively true, but doesn't capture the apparent contradiction present in the original example.
You seem to talk about Menger's view of marginalism, but Menger isn't really part of the classical branch I am talking about: he founded the Autrian School and was pretty skeptical about the neoclassic school at its time.
I suppose you could be right. My understanding is that literally that is what marginalism is. Where are you getting the idea that there are multiple branches of it?
> Where are you getting the idea that there are multiple branches of it?
That's common economics history: Marginalism was “invented” by Jevons and Menger pretty much at the same time (and Walras came a bit later with no prior knowledge of the two others' work at time of writing).
Jevons' work lead to the birth of the neoclassical school, while Menger's founded the Austrian school, and those two where pretty antagonistic for a while (One of Keynes' biggest achievement is probably the reconciliation these two branches in order to fight against his legacy ;).
This isn't accurate. Whatever Jevons and Menger thought of each other, the Austrians and the British were not completely distinct schools. People would call both groups "neoclassical".
The Austrian school in the modern sense only broke with the mainstream with Keynes. They had their own alternate explanation of the Great Depression that never caught on. I think the leaders of the school just moved to the US and became increasingly dogmatic, so modern Austrianism is a small niche.
There was a more recent form of macro that is anti-Keynesian that can be called "neoclassical", which would be the real business cycle theory, but it doesn't owe much to the modern Austrians. If you want to identify it with a specific marginalist, it's closest to Walras.
Marginalism is saying something much more precise than that. It is saying that (in the given example) the two people value their marginal dollars differently than they value one marginal unit of coffee. A statement which is certainly objectively true, but doesn't capture the apparent contradiction present in the original example.