I didn't know anything about this and found the article hard to understand at first, but thankfully the Wikipedia articles on the subject are pretty okay: https

I didn't know anything about this and found the article hard to understand at first, but thankfully the Wikipedia articles on the subject are pretty okay: https://en.wikipedia.org/wiki/Sonnenschein%E2%80%93Mantel%E2%80%93Debreu_theorem https://en.wikipedia.org/wiki/Sonnenschein%E2%80%93Mantel%E2... The very abbreviated TL;DR of this post is: 1. We are taught that markets look like this: https://upload.wikimedia.org/wikipedia/commons/8/8c/Supply-demand-equilibrium.svg https://upload.wikimedia.org/wikipedia/commons/8/8c/Supply-d... 2. By applying rigorous math ("general equilibrium theory"), it turns out that there is no reason that markets can't look like this instead: https://upload.wikimedia.org/wikipedia/commons/a/ab/SMD_Demand_Curve.svg https://upload.wikimedia.org/wikipedia/commons/a/ab/SMD_Dema... 3. OP's article summarizes how economists have reacted to this problem.