There are many conflicting online sources when it comes to determining whether to use “who” or “that” in a sentence. However, one rule is absolutely clear:
- “Who” should be used only when referring to people.
- “That” can be used for referring to people and objects/subjects.
There are two very reliable sources that let us know “who” and “that” are interchangeable when it comes to referring to people:
The first is Jean Yates, who says in her book, The Ins and Outs of Prepositions:
An adjective clause can identify a noun. The clause comes right after the noun.
TO IDENTIFY A PERSON, AN ADJECTIVE CLAUSE CAN BEGIN WITH WHO(M), THAT,
The man who(m) …
The man that ….
The people who(m) …
The people that …
Secondly, the Merriam Webster dictionary, which says of “that”:
a : the person, thing, or idea indicated, mentioned, or understood from the situation b : the time, action, or event specified c : the kind or thing specified as follows d : one or a group of the indicated kind
Using “Who” In The Singular Person
In the singular person, it is preferable to use “who”. For example:
Peter, who was a fine marksman, shot the thief with expert accuracy.
Because you wouldn’t say:
Peter, that was a fine marksman, shot the thief with expert accuracy.
However, you can use “that” on occasion for the singular person. A writer might do this when referring to someone they don’t know personally or have a name for. For example:
The guy that came to fix my water pipes last year said the pipes were very worn.
Using “Who” and “That” In The Plural
In the plural, we can use “that” or “Who”. For example,
Men that act in this way are quite despicable.
Men who act in this way are quite despicable.
As a general rule of thumb use “who” in the singular person, and use “who” and “that” where appropriate in the plural person. But never use “who” to indicate an object/subject, instead use “that” for that purpose.