Much has been made of the distinction between 'that' and 'which' in English, but it can mostly be summed up in two points: 1. 'That' doesn't work so well with commas. 2. 'Which' doesn't work so well with people. David the Grammarian...

David and Paige, KA's resident grammarians, cover appositives and how to use commas along with them.