When using 'that' or 'which' Word often indicates 'incorrect grammar'...when
is it appropriate to use 'that' vs. 'which'?
It depends on where you are to some extent. In UK English they are more
or less interchangeable, but in American English they aren't.
SOURCE:
http://www.wsu.edu/~brians/errors/which.html
I must confess that I do not myself observe the distinction between
³that² and ³which.² Furthermore, there is little evidence that this
distinction is or has ever been regularly made in past centuries by
careful writers of English. However, a small but impassioned group of
authorities has urged the distinction; so here is the information you
will need to pacify them.
If you are defining something by distinguishing it from a larger class
of which it is a member, use ³that²: ³I chose the lettuce that had the
fewest wilted leaves.² When the general class is not being limited or
defined in some way, then ³which² is appropriate: ³He made an iceberg
Caesar salad, which didn¹t taste quite right.² Note that ³which² is
normally preceded by a comma, but ³that² is not.
