When to use "that" or "which"

Hi, I'm sure there is a rule I learned but have long forgotten on when to use "that" or "which" such as...

He picked up the whip which was on the bedside table or

He picked up the whip that was on the beside table.

Thanks for any help and sorry if this is the wrong place for this kind of question. *s* ashley

If I recall correctly, "that" is for restrictive clauses while "which" is for non-restrictive ones, i.e. you use "that" when your relative clause narrows down the preceding statement and "which" when it simply adds to it. But I tend to mix that up all the time, and nobody has ever complained ;)

The car that hit me was white.
The car, which looked brand new, was faster than my bike.

Basically, it all boils down to commas. If I need commas (which are, in turn, just a shortcut for appending a relative clause with "and", making the main clause and the relative clause equally important) I use "with".

Thanks, DarkPoet. Your explanation is concise but reminds me why I forgot the rule. The English language can give me a headache! I may just try to avoid those words altogether. LOL Thanks for taking your time in replying to my question. - ash