Stop telling people DATA is plural

The word data is almost universally used as a singular mass noun in English except among many professional writers and academics who insist that it is the plural of datum, a word that is almost non-existent in English outside discussions of whether data is a plural. The reason usually cited for treating data as a plural is that it was a plural in Latin, which is true but irrelevant since grammatical changes often occur when words are borrowed from one language to another. A perfectly analogous example is the word spaghetti which is a plural count noun in Italian but very clearly a mass noun in English, which is why native speakers of English say This spaghetti is cooked and not These spaghetti are cooked.

Another reason to be suspicious of this alleged rule is that native English speakers generally have to have it drummed into them at school instead of just picking it up naturally like nearly every other plural form in the language. This strongly suggests that it is a socially imposed rule rather than part of the language proper.

Inconsistencies of usage also suggest there is a lot of awkward self-editing going on when people attempt to use data as a plural. Socialization of the rule is successful in getting researchers to write things like These data are... in academic papers which would be appropriate for a plural, but the very same writers will treat it as a mass noun when they ask how much data they have where we'd expect how many data. They also use it as a mass noun in phrases like data gathering, data point and data visualization where we'd expect datum gathering, datum point, and datum visualization.

Writers who insist data is a plural invariably find themselves using it as a singular mass noun in at least some of these cases without realizing it. Nevertheless, people who succeed in showing that they think data is a plural and treat it like one in certain recognizable contexts are widely considered to be following educated usage, and copy editors will often 'correct' writers who don't indulge this fancy.

See also:

The Grammar of Mass and Count Nouns

On Falling Apples and Whether Tomatoes Really are Fruit