We use relative pronouns to avoid repeating the subject (person, place or thing) many times and to be more concise.
who – used for people
- Patients who have been in motor vehicle accidents often have leg injuries.
- Dr. Marks is the surgeon who will perform your surgery.
which, that – used for things
- This is a model of the new shoulder joint that you’ll get.
- The abdomen is soft which makes it susceptible to trauma in motor accidents.
where – used for places or events
- You’ll be followed up in out-patient clinic where the surgeon will check your healing.
- You’re going to radiology where you’ll have a chest X-ray and MRI.
whose – to show possession or belonging
- There are patients whose joint prostheses last 20 years.
- There are some accident victims whose internal injuries don’t show up immediately.
Punctuation with ‘which’, ‘that’ and ‘who’ relative clauses
The part of the sentence with the relative pronoun is called the relative clause.
- Here’s a model of the new shoulder joint that you’ll get.
- You’re going to radiology where you’ll have a chest X-ray and an MRI.
If the sentence makes no sense without the relative clause (it is a defining relative clause), there is no comma before the pronoun.
- Here’s a model of the new shoulder joint that you’ll get. – (“This is a model of the new shoulder joint” doesn’t give any important information -> there is no comma before “that”.)
If the relative clause gives extra information but does not affect the meaning of the sentence (it is a non-defining relative clause) then the relative clause is separated by commas.