How a price forms

Demand, in classroom words, is how much people are willing and able to buy at each price, other things held still. It is a schedule, not a feeling. “I really want it” is a mood. A schedule asks: at this price, how many, and at that price, how many. If income, tastes, or the price of a cousin-good change, the whole schedule can shift. That shift is not the same as sliding along the schedule.

Other things held still is the ceteris paribus habit. Alfred Marshall’s Principles of Economics (1890) is the usual English-language door to that habit on a supply-and-demand page. Nominative: Marshall’s book stays with Marshall. Other-things-still is a teaching freeze-frame. The land does not freeze. Mixing the freeze-frame with a live headline is how a person thinks one print proved a law.

A downward-sloping demand schedule in the usual picture says: at a higher price, people buy fewer units of this thing, holding the rest still. Exceptions get named later (Giffen, Veblen) as curiosities, not as a dare to ignore the usual slope. We will not hunt a Giffen good so you can size it.

Human: a delayed last on this board is one meeting. It is not the demand schedule. If a friend says “everyone wants Apple,” ask at what price, and compared with what. Moods do not have a quantity.