Australia's federal government has set a long-term target for how many adults should hold a qualification gained after school. New survey evidence sits awkwardly beside it, because nearly half of the country's workers now describe themselves as overeducated for the jobs they do. That makes it fair to ask whether the target makes sense.

People decide to study for many different motives. Getting a job, the prospect of better pay and a wider set of employment options all come into it. Those job- and pay-related motives are not the only ones that matter. Some people also study because a subject interests them, or because they want to find out what it could lead to. Recent research suggests that, in choosing a course, people appear to put their own interests ahead of what the course costs or what they might later earn.

How well a qualification fits a job may also depend on when the question is put. Workers may sense a weak fit between their qualification and their current job, especially when economic conditions are bad, yet they may judge that fit differently at another stage of their working life. A bachelor's degree may lie behind a whole career rather than a single job within it.

Economics itself contains rival theories of education's purpose. Gary Becker, an economist, was well known for his interest in "human capital", by which he meant whether people hold the skills and experiences that a particular job demands. On that view, a qualification supplies a specific bundle of skills matched to a specific job. Other economic research maintains that a qualification can work in quite another way, signalling to employers that an applicant is a "good" candidate, someone who meets deadlines and can work on long-term projects and under pressure. Understood in that second way, holding a degree is less about possessing particular skills and more about building and showing broader capabilities.