A way to decide whether to use 'that' or 'which':i am not sure if this has been covered, but misuse of That, Which and Who is really annoying me.
Inanimate objects (things) can be that , or which , but People are who.
Eg. I have a friend that went to my old school , should read "who" went to my old school.
'That' describes; 'which' defines.
'Which' tends to be commonly used for both.