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.