Grammar question: when do you use "that", and when do you use "which"?

[ejt1764]

I know how to use them, but dh is doing corrections on a report, and, although I can correct it myself, I can't explain it to him.

Help please ....

Here

Basically, if you're using the phrase to identify something, you use 'that'. If you're using it to be descriptive, you use 'that'.

So:

1. The horse that I am looking for is over there.

2. The horse, which is funny-looking, is over there.

brilliantly succinct, thank you!

Ugh, should have said, if you're using it to be descriptive, you use 'which'.