Demand is to price as supply is to what?

Demand is a function of price, meaning that for each price level we can see how much people want to buy. Supply is a function of quantity, meaning that for each quantity level we can see how much producers are willing to sell. So the relationship is: Demand is to price as supply is to quantity. For example, if the price of coffee rises, people buy less (demand drops), while if the quantity of coffee produced increases, producers are willing to sell more at each price (supply rises). This shows how each curve links a different variable to the market.