Relative pronouns—who, whom, which, that, where, when, and whose—introduce clauses that describe a noun, and the ACT tests whether you picked the right one and set it off with commas when the clause is extra information. Most misses come from mixing up who/whom or using which without commas when the clause is essential.
Who vs whom (people only)
Who acts as subject (before a verb); whom acts as object (especially after a preposition). Use the he/him test: if you would say he, choose who; if him, choose whom. "The student who scored highest" → "He scored." "The counselor to whom I spoke" → "I spoke to him." Full case rules live in ACT pronoun case.
Which vs that (things and ideas)
- That + no commas: restrictive clause—the info is required to identify the noun. The book that I borrowed is due Friday.
- Which + commas: nonrestrictive clause—extra detail you could remove. My chemistry textbook, which has a torn cover, is still usable.
Comma placement is the giveaway. Review ACT comma rules if comma pairs trip you up.
Where, when, and whose
Whererefers to places only—not abstract situations ("the stage where we rehearsed," not "a situation where confusion arises" when in which is cleaner). When refers to times. Whose shows possession and works for people and things: the author whose essay won.
In which for media and abstract nouns
For books, articles, studies, and abstract ideas, in which often beats where or that: the article in which the researcher explains her method. The ACT prefers precise, formal relative clauses here.
How to solve fast
- Identify what the clause describes—person, place, time, or thing.
- Ask whether the clause is essential (no commas) or extra (commas).
- Run the he/him test for who/whom; eliminate mismatched pronouns.
Relative clauses often sit inside independent and dependent clauses. For the full grammar map, see ACT English grammar rules.
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