For more about commas see our Punctuation Overview page.
A complex sentence is one that consists of a main clause and at least one subordinate clause. When writing complex sentences, commas are used to separate clauses.
Being alone in the house, Sally was feeling afraid.
I first tried tapas in Spain, whilst l was on holiday.
In the sentences above, the intended meaning would remain if the subordinate clauses were to be removed.
Though this level of information is probably sufficient in the primary classroom, it is worth noting that there are different types of subordinate clauses. Some of these clauses do not require commas to separate them from the main clause…
A subordinate clause that begins with ‘who’, ‘whom’, ‘which’, ‘where’ or ‘that’ is known as a relative clause. A relative clause may be a restrictive relative clause or a non-restrictive relative clause.
Here is an example of a restrictive relative clause.
People who have ticket numbers between l and 50 may come to the front of the queue.
A restrictive relative clause contains information that is essential to the meaning of the sentence. In the example, if you take out the clause ‘who have ticket numbers between 1 and 50’ then the whole point of the sentence is negated. This is a restrictive relative clause.
A restrictive relative clause should not have commas placed round it.
Here is an example of a non-restrictive relative clause:
Simon, who was simply not tall enough, could not ride on the roller coaster.
In this example the clause ‘who was simply not tall enough’ is a non-restrictive relative clause. If it were to be removed, it would not significantly alter the meaning of the sentence. This is similar to the way in which commas are used like brackets in a previous section.
As a rule of thumb, if you can’t miss out the clause then you can leave out the commas…