The words that, which, who, whom, or whose are called relative pronouns.
Watch this introductory lesson or this extended lesson on relative pronouns and relative (adjective) clauses in our LC elearning modules class in D2L.
Rules for Relative Pronouns
Rule 1. Use who or which after a noun to give more information about a person.
Example: The doctor, who operated on me, has left here and works at Hamad Heart Unit.
Example: As school nurse, I had students with infectious diseases, which led to infection of other students.
Rule 2. Use whose as the possessive form of who.
Example: This is Doctor Khalid, whose brother studied with me at UCQ.
Rule 3. Use whom as the object of a verb or preposition.
Example:This is Doctor Khalid's brother, with whom I studied with at UCQ.
Rule 4. Use that or which after a noun to make it clear which thing you are talking about.
Example: The nursing team that does the most operations in this hospital will win the award.
Rule 5. Use which as a subject or object of a relative clause..
Example: The new ICU, which will be built at Hamad Hospital, will provide better service for Qataris.
Videos
Watch this 9-minute introduction to using relative pronouns.
English With Ashish. (2019, September 2). Relative pronoun -- Which vs that -- Defining and non-defining clause -- Relative clause [Video]. YouTube. https://www.youtube.com/watch?v=imEtjZ1EgOI
Watch this 19-minute extended lesson on using relative pronouns.
LetThemTalkTV. (2021, April 17). Relative pronouns -- That, which, who(m), whose, where, when or nothing? -- Explained with donuts [Video]. YouTube. https://www.youtube.com/watch?v=meEVMzel0kQ
More Information
"Relative Pronouns", Butte College.
See your APA manual, p. 121-123 (4.19 "Pronouns for People and Animals," 4.20 "Pronouns as Subjects and Objects," 4.21 "Pronouns in Restrictive and Nonrestrictive Clauses," 4.22 "Subordinate Conjunctions").
Reference
American Psychological Association. (2019). Publication manual of the American Psychological Association (7th ed.). https://doi.org/10.1037/0000165-000