The minimum wage is a contentious issue among economists, and yet it enjoys near-universal support among the public. In my view, public views of the minimum wage are simply the result of a lack of careful thought by most people. Daniel Kahneman’s theory that people, when faced with a difficult question, substitute a simpler question that they can easily answer, applies particularly well in this case. People answer the question of whether they would like people to earn more when the real question is whether government should mandate higher wages (I first heard this argument from Bryan Caplan on EconLog).
A purely empirical argument for or against the minimum wage is methodologically wrong-headed because empirics do not speak for themselves. Sound theory must be the economist’s first tool in understanding the effect of a policy such as the minimum wage.
Before we can understand something like the minimum wage, we must understand the role of prices in allocating factors of production to their various uses. The price of a factor signals to entrepreneurs that that factor is scarce, that it is needed elsewhere in the economy, and that the entrepreneur who can reduce his usage of relatively more scarce factors in favour of relatively less scarce ones can earn profits, while entrepreneurs who fail to do so earn losses. I give the example of a sandwich shop during an oil boom; the high price of labour caused by the oil boom leads the sandwich shop to substitute away from labour in various ways.
The oil boom in my illustration is irrelevant to the story. The sandwich shop would adapt to an increased price of labour no matter what caused it. If the cause is a minimum wage law, the people no longer employed making sandwiches are involuntarily unemployed rather than finding employment in some other industry.
Minimum wage opponents sometimes get into trouble when they draw supply and demand curves to illustrate the impact of the price floor. The problem with this is that supply and demand diagrams come with built-in assumptions that do not hold true in the case of labour markets. Low-skilled labour is not a homogeneous quantity being sold in a centralized market. The simple supply-and-demand story does not capture all the effects of the minimum wage. For instance, firms substitute between different sorts of workers affected by the minimum wage. In addition, the other terms of employment contracts can change in response to a minimum wage law, such as training and benefits.