Government of Canada
Symbol of the Government of Canada

Commas with an adjective clause

Question:

Do I need commas around the adjective clause in the sentence below?

The woman who became Canada’s first licensed female pilot was born in Wiarton, Ontario, in 1908.

Answer:

No, you don’t need commas, because the clause is giving essential information that serves to identify the noun woman: it tells the reader which woman you mean. Without it, the sentence would not be clear:

The woman was born in Wiarton, Ontario, in 1908. [What woman?]

When a clause is essential, it is too important to the meaning to be separated from the noun it modifies. Therefore, the clause is not set off with commas.

But if the woman were already identified—if you named her, for example—the clause would become non-essential:

Eileen Vollick, who became Canada’s first licensed female pilot, was born in Wiarton, Ontario, in 1908.

or

Eileen Vollick is a key figure in Canadian aviation history. This woman, who became Canada’s first licensed female pilot, was born in Wiarton, Ontario, in 1908.

Here, the clause provides secondary information that is valuable and interesting but not essential to the meaning. When an adjective clause gives non-essential information, we set it off with commas, as in the last two examples.