The question often arises whether that, as a relative pronoun, may refer to people as well as things. The better authorities say yes — that this use of that is part of Standard English. The OED notes that that is a “general relative pronoun . . . referring to persons or things” and shows that it dates back some 1,300 years in English.

As an empirical matter, although the phrasing people who is much more common today in print, people that is equally frequent in the conversation of English speakers. This might suggest that people that is a less formal wording. But calling it “incorrect” is surely wrong.

Seemingly the first English-language grammarian to address the point was Daniel Turner in 1739. He wrote: “The word that may be used instead of who or which as a relative; as, the pen that, or which, you made; the man that, or who, came.” Others soon followed suit. The influential Robert Lowth wrote in 1762: “That is used indifferently both of persons and things.”

Lindley Murray, known as “the father of English grammar,” first published his famous grammar in 1795. He was the most thorough commentator on this point in the early days. He found instances in which that is the preferred relative for people, usually where a restrictive relative is required:

The pronoun that is frequently applied to persons as well as to things; but after an adjective in the superlative degree, and after the pronominal adjective some, it is generally used in preference to who or which; as “Charles XII king of Sweden, was one of the greatest madmen that the world ever saw.” . . . ‘He is the same man that we saw before.’ There are cases wherein we cannot conveniently dispense with this relative as applied to persons; as first, after who the interrogative; ‘Who that has any sense of religion, would have argued thus?’ Secondly, when persons make but a part of the antecedent; ‘The woman and the estate that became his portion, were too much for his moderation.’ In neither of these examples could any other relative have been used.

Because that is used as a restrictive or defining relative, it would almost never be used with a person’s name. Hence I’m talking about Joan, who showed up early. Only if there were two or more people with the same name would a restrictive use be necessary to identify which person is being referred to: Do you mean the Joan that lives down the street?

What do more modern commentators say? Very much the same thing, on the whole. For example:

1928: “That is used when referring to persons, animals, and things without life. That is preferred (1) when the antecedent is qualified by a superlative adjective <He is the most daring man that I have ever seen>; (2) when the antecedent includes both persons and things <Where are the tents and the hunters that I saw?>.” (Mason Long, A College Grammar)

1966: “The relative that refers to persons quite as naturally as to things, and quite as naturally as who refers to persons. . . . We are, then, free to use that instead of who for a sign of the restrictive clause about persons.” (Wilson Follett, Modern American Usage)

1980: “That for who is sometimes objected to, but the objection has no basis. Random House says that may refer to a person, and so do American Heritage and Webster.” (Roy H. Copperud, Ameri­can Usage and Style)

But there is a contrary line of authority. It may have begun with James Buchanan (not the 19th-century president but the 18th-century grammarian), who wrote in 1768: “That is often used, but inelegantly, for who, whom, and which; as, This is the Man that bought the Horse, for who bought the Horse. He is the Man that (for whom) I met in the fields.” Note that the charge is merely that the usage is “inelegant,” not wrong. Historically, this notion appeared only sparsely in grammars and stylebooks, but it surged in the 1980s, increasingly with a sense that the “people” usage is erroneous. For example:

1980: “Please use who instead of that or which to refer to people. Slightly rude: The students that come to class make my heart jump with joy. Polite: The students who come to class make my heart jump with joy.” (Sally Foster Wallace, Practically Painless English)

2002: “For people, use who or whom. For objects, plants and animals, use that or which.” (Paul R. Martin, The Wall Street Journal Guide to Business Style and Usage)

Wallace’s view that who seems more polite than that is worth considering in any given context. The view is that who makes it personal, and that impersonal. Still, on the whole this line of authority is simply ill-considered on the people/things point.

Yet it has been influential. In a Twitter poll conducted in September 2021, I posed this question: “Is it your understanding that (A) the relative that can refer to people or things, or (B) who must be used with people, never that?” The results: 44 percent for (A), 56 percent for (B). However common the notion in (B) might be, it must be classed as a linguistic superstition. It simply has no solid foundation in history, grammar, or reason.

One little advantage of the relative that, by the way, is being able to avoid the who/whom choice. It’s your readers that you must think of. Do you really want to say or write, It’s your readers of whom you must think? The question often arises.