Difference between that and which

This is the fifth part of the difference between series.

Two words commonly confused with each other are “that” and “which”. So much so that it has become common in many circles to not differentiate between the two. As a result, some people may disagree with my explanation. Nevertheless, I offer it here for some background and for anyone who considers himself a purist.

The difference between the two is “that” accompanies a restrictive clause and “which” is used for non-restrictive clauses.

What’s a restrictive clause? It’s a set of words necessary to understand what a person means. For example:

I live in the house that Jack built.

If we left out the phrase “Jack built”, the reader may not know which house we meant. It restricts the meaning.

On the other hand, if most readers were already familiar with the house we mentioned, then we would use “which”.

I live in the house, which Jack built.

The phrase “I live in the house” could stand alone, but we add “Jack built” for extra information.

To sum it up, if the information is important to know, use “that”. Otherwise, use “which”. Remember though that “which” is always preceded by a comma.

Let me know if you have any grammar questions, and I’ll be sure to post the question and answer here.