This one is about as simple as it gets: A human being is a “who.” Everything else is a “that” or a “which.”
But what happens when you have a collection of human beings? Confusion is what happens.
While running for president back in 2011, Mitt Romney took a lot of flak for saying, “Corporations are people, my friend.” While a corporation may be the totality of the people it employs, the corporation itself is not a person. Except when it is. Because, in the United States at least, there is such at thing as corporate personhood. It means that corporations have some of the same rights as human citizens, including free speech. (On the other hand, try to arrest a corporation for destroying property or killing people. Go head, you just try.)
So you’ll see mainstream publications such as MarketWatch write, “SEC targets companies who use made-up accounting metrics.”
What if it’s not a big, faceless corporation that we’re talking about, but a one-man plumbing business? The lone plumber is the entire business, after all.
Then there are sports teams. It’s common to see sentences like “The Miami Heat, which is oozing with superstars…” But you also get sentences like, “The Pittsburgh Steelers, who have the No. 25 draft pick…”
From there it’s only a short hop to alumni association, occupations, age groups and the like.
Sorry to say, there is no hard and fast rule on which everyone agrees.
Even Henry Fowler, who could get pretty stuffy regarding the English language, took a nonchalant view on this. “The relations between that, who, and which have come to us from our forefathers as an odd jumble, and plainly show that the language has not been neatly constructed by a master builder who could create each part to do the exact work required of it, neither overlapped nor overlapping; far from it, its parts have had to grow as they could.”
In general, Fowler doesn’t want to deny the humanity of specific persons, but he’s willing to get impersonal when talking about a generic type of person.
“Expressions in which we may prefer that without being suspected of pedantry are: The most impartial critic that could be found; The only man that I know of; Anyone that knows anything knows this; it was you that said so; Who is it that talks about moral geography?”
That’s why author Edgar Rice Burroughs (he invented Tarzan) was on safe ground titling one of his books “The People That Time Forgot.”
As you may have gathered, Henry Fowler came from an age and culture where gentlemen could ruminate on such matters over brandy and cigars in a dark paneled library after dinner. You, on the other hand, are more likely to need a quick rule of thumb. So here’s one:
Refer to humans as “who,” even in groups. Refer to non-human entities as “that,” even if humans are members or employees. If you have a mix of the two, “that” will have to do.