I am trying to reconcile chapter 5 with chapter 1. Both chapters find the equilibrium price and quantity, but chapter 1 uses demand and supply curves and chapter 5 uses demand and cost curves. Why does chapter 5 not mention supply curves at all?

What is the supply curve?

It is the graph of the corresponding price, for each given quantity, that maximizes the profit for the producer. The equilibrium Quantity and Price (Q & P) is the Q & P that is on both the supply and demand curves.

In chapter 5, what are we doing?

We are finding the point on the demand curve (Q & P) that maximizes profit for the producer. This is precisely the point on the demand curve that is also on the supply curve.

We could then construct the entire supply curve by using the method of chapter 5 (marginal revenue = marginal cost). We would create a series of fictitious (non-intersecting) demand curves, each successively higher, then find the point of maximum profit for each demand curve. These points would then constitute the supply curve.

[NEAS: Well-reasoned analysis. Landsburg's intention is more subtle, as he explains in later chapters. The cost curve is the supply curve in a competitive market. In a monopolistic or oligopolistic market, the firm still maximizes profit by equating marginal revenue to marginal cost, but the equations become more complex.]