Which and That

[mynhauzen]

What is the difference in "Which" and "That", and what is the way to know which one is the best to use?

(I dont know if this topic was discussed.. i tried to use search, but I'm not sure if it works here)

[Auzbee]

If you have Manhattan SC guide, it explains it well.
'Which' - used to introduce non essential modifiers. Means that a modifier introduced by 'which' can be removed without loosing any essential meaning.
'that' - used to introduce essential modifiers.

Read up the Modifiers section in the SC guide for examples and explanations.

[Danielle]

Auzbee's right on target, although the particulars on which/that are very involved. It's important you find a source (manhattan SC works really well) that goes over this in detail and offers practice exercises because the GMAT tests this knowledge over and over.