Cambridge economist Joan Robinson attacked the theory in similar line, arguing that the concept is circular: "Utility is the quality in commodities that makes individuals want to buy them, and the fact that individuals want to buy commodities shows that they have utility"  :48 Robinson also pointed out that if we take changes in peoples' behavior in relation to a change in prices or a change in the underlying budget constraint we can never be sure to what extent the change in behavior was due to the change in price or budget constraint and how much was due to a change in preferences.  [ better source needed ]
The law of supply and demand is the theory explaining the interaction between the supply of a resource and the demand for that resource. The law of supply and demand defines the effect the availability of a particular product and the desire (or demand) for that product has on price. Generally, a low supply and a high demand increases price, and in contrast, the greater the supply and the lower the demand, the lower the price tends to fall. BREAKING DOWN 'Law Of Supply And Demand' One of the most basic economic laws, the law of supply and demand ties into almost all economic principles in one way or another. In practice, supply and demand pull against each other until the market finds an equilibrium price. However, multiple factors affect both supply and demand, causing them to increase or decrease in various ways.