Common sentence problems: Relative clauses
Examples (1–4) represent some common mistakes with relative clauses. Read more about the difference between restrictive and non-restrictive relative clauses here.
Use a comma with a non-restrictive relative clause
Incorrect
(1a) City traffic means a great deal of accelerating which requires power to get the car moving quickly.
Correct
(1b) City traffic means a great deal of accelerating, which requires power to get the car moving quickly.
Use two commas with a non-restrictive clause
If you use a non-restrictive clause to add information in the middle of a clause, remember to use two commas – one at the start of the relative clause, one at the end:
Incorrect
(2a) The lecturer, who is very experienced explains everything clearly.
Correct
(2b) The lecturer, who is very experienced, explains everything clearly.
Do not use a comma with a restrictive relative clause
Incorrect
(3a) There are a number of programmes, that allow modelling of the data.
Correct
(3b) There are a number of programmes that allow modelling of the data.
Do not separate the relative clause from its referent
A relative clause cannot be separated from the thing or person that it refers to. In (4a), the sentence means that the course, not the figure, illustrates the types.
Incorrect
(4a) This figure is from a course in Materials Science which illustrates three different types of material structure within metals.
Correct
(4b) This figure, which illustrates three different types of material structure within metals, is from a course in Materials Science.