Neoclassical economics
The essence of Shackle's radical reevaluation of economic theory was primarily epistemic. He thought that neoclassical economics and other forms of economics that use equilibrium methods ignored the dimension of time. Neoclassical economics relies on the idea that agents will act rationally; but this rationality is effectively synonymous with saying that agents know the future. Shackle pointed out that in order for agents to act "rationally"—in the sense that neoclassical economists understood that word—they would have to logically know what actions all other agents were going to undertake. This, Shackle claimed, was effectively the same as assuming that they knew the future. Shackle maintained that the way that neoclassical economics had smuggled in this strong assumption was in its use of simultaneous equations.