Our task then is to discover the laws to which these purchases and sales tend to conform automatically. To this end, we shall suppose that the market is perfectly competitive, just as in pure mechanics we suppose to start with, that machines are perfectly frictionless. Unfortunately, this mild and uncontroversial statement is not very informative. If one sought to pinpoint the feature that distinguishes economics from the other social sciences, one would have to be a bit more precise. All branches of Neoclassical economics feed into or stem from this central procedure.
Exchange is the Neoclassical forest, the rest of Neoclassical economics is but trees.
Alas, in this respect, Neoclassical economics has been somewhat narrow. If demand is not equal to supply, then the prices were wrong. This does not mean that these alternative exchange processes don't have prices at all. If we define prices as the ratios of goods exchanged, then all exchange processes end up with prices, i.e. exchange ratios between goods. The reason for the intense and exclusive Neoclassical focus on the price-mediated exchange priocess is not mere shortsightedness on the part of the Neoclassicals.