It's November, and that means it's NaNoWriMo time again. Are you doing it? I'm attempting again.

In order to myself in gear, I've posted that I'll be fielding questions for anyone who's interested. Mostly it was meant for fans of speculative fiction, but my first question was one for grammar that I hadn't answered yet on this blog (mostly because others have before): what is the difference between which and that?

Here's the answer.

/That/ is generally used for information that is necessary for the information you're providing. Therefore, it's restrictive.

/Which/ is generally used for information that is in addition to the information already provided. In other words, it's nonrestrictive.

In short, /that/ is used when defining material. /Which/ is used when elaborating upon material without defining it.

For example:

The house next door, which I didn't know was vacant, burned down yesterday.

The house is defined as being both 'next door' and 'having burned down'. It's not necessary to know that the author didn't know it was vacant. That information is in addition to.

The house that burned down yesterday was vacant.

It's relevant to know what house was vacant. We restrict the clause /burned down yesterday/ with the use of /that/. In this case, we define the house as being 'the one that burned down'.

Another good discussion on the topic is here. It even has exercises. They also make a note about using Who in restrictive and nonrestrictive clauses. It's important to note that a lot of people misuse /which/ or /that/ in place of /who/. The latter two are used for things, /who/ is used for people. Give people the proper respect of being alive and requiring the pronoun /who/.

Thanks to Sydust on NaNo for the question. Keep them coming.

PS - I'll be answering genre-related questions over at my other blog for those who are keeping track of things.