Criteria is plural. Criterion is singular. Although most dictionaries and usage authorities still make this distinction, criterion is likely to go the way of datum and agendum (which are only used by fastidious English users). No matter how hard we fight the change, criteria will become singular.
We don’t recommend using criteria this way—mainly because some readers might consider constructions like this criteria and my main criteria is to be wrong—but English eventually imposes its own rules on words derived from other languages.
Examples
For now, though, most edited publications still use criterion for the singular noun meaning a standard by which something can be judged—for example:
Williamson implies that’s so, rendering this a meaningless criterion. [Washington Post]
Perhaps one such criterion was for mortgages to have a loan-to-value ratio of 100%. [The Atlantic]
If comfort were the top criterion for selling womenswear, Jimmy Choo would be out of business. [New York Magazine]
Criteria functions as a plural noun:
We’ll look for help today with today’s screen from Morningstar CPMS, which has set up a conservative screen using seven criteria. [The Globe and Mail]
The new criteria have been attacked by many in the industry as being too onerous. [Financial Times]
Although criterion lives, criteria is gaining ground as a singular noun. Here are a few example out of many:
Careful though… this criteria is a double edged sword. [Schriever Air Force Base]
The only criteria is that it must be partially or completely open to the public. [Houston Business Journal]
Dark matter is another criteria that is examined. [Universe Today]
