Credential inflation is the rise in educational requirements for jobs as a rising proportion of the population attains more advanced degrees. The value of a given educational certificate or diploma declines as more people have one, thereby motivating them to stay in school longer. In the United States, high-school (i.e., twelve-year secondary school) diplomas were comparatively rare before World War II; now high-school degrees are so commonplace that their job value is worthless. University attendance is now over 60% of the youth cohort, and is on the way to the same fate as the high-school degree. It is a worldwide trend; in South Korea, 80% of high-school graduates now go on to higher education. The main thing that inflated degrees are worth is to plough them back into the educational market, seeking still higher degrees. This in principle is an endless process; it could very well reach the situation of the Chinese mandarin class during the later dynasties, when students continued sitting for exams into their thirties and forties— only now this would affect the vast majority of the population instead of a small elite. Different countries have gone through educational inflation at different rates, but from the second half of the 20th century onward, all of them have followed this path.
Educational degrees are a currency of social respectability, traded for access to jobs; like any currency, it inflates prices (or reduces purchasing power) when autonomously driven increases in monetary supply chase a limited stock of goods, in this case chasing an ever more contested pool of upper-middle-class jobs. Educational inflation builds on itself; from the point of view of the individual degree-seeker, the best response to its declining value is to get even more education. The more persons who hold advanced degrees, the more competition among them for jobs, and the higher the educational requirements that can be demanded by employers. This leads to renewed seeking of more education, more competition, and more credential inflation.