Asking whether supply or demand sets price is like asking which scissor blade cuts
Economist Alfred Marshall compared the debate over what determines price, the cost of making something, or how much buyers want it, to arguing over which blade of a pair of scissors does the actual cutting. Neither blade cuts alone; neither factor sets price alone. Marshall's 1890 synthesis showed that supply and demand jointly determine both price and quantity, settling a long dispute between economists who insisted one side or the other had to be the real cause.