The Supply of Labor

Every hour you work is an hour of leisure you gave up. That's the trade-off behind labor supply. When the wage rises, working an hour pays more than before, so leisure gets more expensive to hold onto. People respond by offering more hours, and new people who weren't willing to work at the old wage now are. Stack up everyone's individual decision and you get the market labor supply curve: upward sloping, wage on the vertical axis, quantity of labor on the horizontal.

Now zoom into one firm in a competitive labor market, say one of thousands of firms hiring accountants. That firm is a tiny buyer next to a huge pool of workers. It can hire one more accountant, or ten more, without budging the market wage at all, because its hiring is a drop in the bucket. So from that single firm's point of view, labor supply looks perfectly flat: it can get any quantity of workers it wants at the going wage, and the wage it pays doesn't change as it hires more. That flat curve is a firm-level fact, not a market-level one.

This is the same logic as a perfectly competitive firm facing a flat demand curve for its output: small player, big market, no power to move the price. At very high wages, the trade-off can bend backward: once someone is earning enough, extra income can make leisure feel more valuable, and hours worked actually fall even as the wage keeps climbing. That sits just past the basic upward-sloping story, and it sets up how firms, facing that flat supply curve, decide how many workers to hire by comparing the wage to what an extra worker adds to revenue.