labour supply and the work-leisure trade-off

There are only 24 hours in a day, and every hour spent earning money is an hour not spent sleeping, with family, or doing anything else you enjoy. Deciding how much to work is therefore a trade-off between two good things: income from work and free time, which economists bundle together as 'leisure'. Labour supply is the answer people give to this question — how many hours, at a given wage, they are willing to offer in the labour market.

The trade-off has a hidden price tag. Every hour of leisure costs you a wage you could have earned — that is its opportunity cost. So when the wage rises, two opposing forces appear. The substitution effect says: leisure just got more expensive, so work more (each hour off now costs more foregone pay). The income effect says: you're richer now, and one thing people buy with extra income is more free time, so work less. Usually at low wages the substitution effect wins and people work more as pay rises; at high wages the income effect can take over, so a few very well-paid people actually choose to work less. This is why the individual labour supply curve can bend backward at the top.

This framework explains a lot of everyday life: why a raise might make a parent cut back hours rather than add them, why retirement, second jobs, and 'I'd rather have the time than the money' all make sense, and why tax changes alter how much people work in hard-to-predict ways (the two effects pull in opposite directions). A caveat: in reality many people can't freely choose their hours — jobs come in fixed shifts, contracts, or none at all — so the neat trade-off is a model of the choice, not always the choice people actually get.