On this language site and others, readers often question a writer’s choice of that instead of who to refer to a person. Here are some typical comments:
As the word “that” [in this sentence] refers to human beings, shouldn’t the relative pronoun be “who”?
English is my second language, and it hurts to see the rampant disrespect everywhere for “a person who.” Why did you write “person that” and not “person who”?
When I see “that” used instead of “who” to refer to people, it alerts me and, sure enough, the prose or speech that follows is usually sub-par.
The use of “that” for “who” is something that has come about due to the lack of education about the topic.
I blame the Americans for starting the habit of using “that” instead of “who” to refer to persons.
It is just plain ugly usage to have the word “that” replace “who.”
Strong convictions can be a good thing, but when it comes to the merits of who and that as relative pronouns with human antecedents, a little historical knowledge is relevant.
relative pronoun: a pronoun that combines the function of a personal or demonstrative pronoun with that of a conjunction, subordinating one sentence or clause to another.
Relative pronouns were a late development in English and other Indo-European languages. According to a note in the OED, Indo-European had no relative pronouns. The earliest form of English managed without them by means of parataxis.
parataxis: the placing of clauses one after another, without connecting words to show the relation between them.
Albert C. Baugh refers to the development of relative pronouns in A History of the English Language:
Refinements in the use of subordinate clauses are a mark of maturity in style. As the loose association of clauses (parataxis) gives way to more precise indications of logical relationship and subordination (hypotaxis) there is need for a greater variety of words effecting the union.
Again quoting Baugh, “[that was] the almost universal relative pronoun, used for all genders, throughout the Middle English period.”
The use of which began to alternate with that in the 15th century. At first, which was used only with neuter antecedents, but was sometimes used with persons. This use of which to refer to persons is reflected in the Protestant version of the Lord’s Prayer: “Our Father Which art in Heaven.”
The use of who as a relative pronoun to refer to people is a development of the 16th century. Many speakers, myself included, feel that who is usually the first choice when the antecedent is human, but recognize that its use is a stylistic choice and not a matter of rule. Sometimes that may be the better choice.
The most that can be said regarding the relative pronouns who, that, and which is this:
Who is for people and which is for things, but that has always stood for either.