E2, I'll share a little "poor man's trick"
that I use to distinguish when to use these two terms (because I am a poor man)
, which provides a mnemonic to remember which term to use.
In addition to CC's excellent explanation ("that" = restrictive; "which" = non-restrictive), here is how I remember:
that: begins with a "t"...in fonts such as Helvetica, a "t" looks like the pointer-needle on a compass...it defines where you are headed. Without a compass needle, you are lost...you
need it to determine where you are going.
Likewise, you use "that" when the description/restriction is
vital to
point out to the listener specifically what you are talking about, and if you leave off the "that..." phrase, the listener won't know for sure the object to which you are referring.
For example,
I like only chocolate-chip cookies that my mother makes
This means "the only chocolate-chip cookies that I like are ones that my mother makes, and no one else's chocolate-chip cookies.
We'll compare/contrast "that" with "which" after we explain a mnemonic for when to you "which".
which: To remember when to use "which", think of the near homophone, "witch"...When a coven of witches gather together, they just gossip about non-essential or extraneous information. Therefore, use "which" when the information that accompanies it is just so much non-essential, additional (perhaps interesting) information, but it is information that is not necessary to clarify the specific subject of the sentence.
Using the previous sample sentence, but replacing "that" with "which", notice how the meaning of the sentence changes:
I like only chocolate-chip cookies, which my mother makes
The meaning here is that I do not prefer eating anything except for chocolate-chip cookies, and, incidentally, my mother happens to bake such cookies. The fact that my mother makes such is simply gossipy, incidental, unneccessary information.
Also notice that when you use "which" in this sense (as incidental, non-restrictive information), we
always show that it is unnecessary information with a preceding comma...That is why, in each case above, I show the comma within the bold-face type...You would not use a comma preceding "that" since such a clause is
vital to the listener's clearly knowing the specific subject to which you are referring.
So, in summary, "that" is a vital pointer clarifying the specific subject of the sentence; ", which" is unnecessary "gossip" that adds spice about the subject, but the spice is not necessary to
restrict whom or what we are talking about.
Does that help a little?
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Mufasa
(aka Dave of Sandy, Utah, USA)
[I provide low-cost, remote Database Administration services:
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