Over the years as a writer and editor (and interrupted linguist), I’ve mellowed quite a bit. From a young age through my late 20s, I was a strict prescriptivist/pedant: “These are the rules; I am going to follow them, and I am going to get an A!” Gradually I’ve shifted toward descriptivism: “All usage is in some stage of flux; I just want to write clearly for my audience, so I can convey ideas as accurately as possible.”
But there’s one usage about which I am adamant: “Data.” Is it singular, or plural? The answer I accept is “Ask your audience.”
Here’s my argument:
(1) Are you speaking or writing Latin? “Data” is plural.
(2) Are you speaking or writing English? Ask yourself: How does my audience expect me to treat “data”?
(a) “Data” is neither singular nor plural in essence, but a mass/uncountable noun (like “furniture” or “traffic”–or “audience.”) Nevertheless,
(b) If you are writing or speaking to an audience of scientists (especially social scientists, but not computer scientists), you should use plural verbs and markers with “data”–otherwise, they will consider you unsophisticated, and possibly think less of your expertise. (I don’t think that’s a fair leap to make, but it’s a fact of life.)
(c) If you are writing or speaking to a general audience and/or computer scientists, use “data” with singular verbs and markers. Otherwise, your audience is quite likely to think you are being pretentious. (If you *want* them to think you are pretentious, have at it. Just be aware of the effect this choice can have.)
(d) If you don’t know enough about your audience to make an informed choice, rewrite the sentence to avoid having to use “data” with a marker of grammatical number.
The argument that “data” is the plural of “datum” holds no weight with me, because:
(i) I can’t remember the last time I heard “datum” (rather than “data point”) in common parlance; and, more importantly,
(ii) English is not Latin. Once English has accepted a word from another language, the grammatical rules of the root language no longer control that word. “Opera” in Latin is the plural of “opus,” but in English “opera” is most frequently used as a singular noun. Most people use “agenda” in English as a singular noun as well–“Do we have an agenda?” “Hold on, I’ll send it to you.”
Come at me.