(j @ Feb. 16 2005,04:49) It's getting there; I do see an improvement. I don't envy you trying to learn English. I was about to offer you a quick object lesson on the difference between usage of "which" (as in your post title) and the word "that", but I decided it would be too confusing (for you and for me.). Maybe in six months?
I am ready.
You only think you are. Have fun with the following: The usage is intimately linked with the distinction which grammarians made between restrictive and non-restrictive clauses. A restrictive clause is one which limits, or restricts, the scope of the noun it is referring to. Take these examples: The house that is painted pink has just been sold. The house, which is painted pink, has just been sold. In the first of these, the clause "that is painted pink" is a restrictive clause, because it limits the scope of the word "house", indicating that the writer doesn't mean all houses, only the one that has been painted in that particular colour; if you take that clause out, we are left with The house has just been sold: we no longer know which house is being referred to and the sentence loses some crucial information. The second example is non-restrictive: the writer is giving additional information about a house he is describing; the clause "which is painted pink" is here parenthetical"”the writer is saying "by the way, the house is painted pink" as an additional bit of information which is not essential to the meaning and could be taken out. Here's another example: Another cause of stress is a traumatic event that is out of the ordinary and has a major impact on the person's life. The argument here is that the clause "that is out of the ordinary and has a major impact on the person's life" modifies and constrains "event". It's not just any event but one specific type of event, to the extent that the whole block from "event" onwards forms one idea. That makes the clause restrictive. Older style guides make two firm points about the difference between the two types of clause: Restrictive clauses are introduced by that and are not separated from the rest of the sentence by commas. Non-restrictive clauses are introduced by which and must be separated by commas from the rest of the sentence to indicate parenthesis. The problem is that few people have followed these rules systematically, and you can find lots of examples where the relative pronoun which is used to start a restrictive clause. The 1965 edition of Fowler's Modern English Usage comments: If writers would agree to regard that as the defining relative pronoun, and which as the non-defining, there would be much gain both in lucidity and in ease. Some there are who follow this principle now; but it would be idle to pretend that it is the practice either of most or of the best writers. This is even more true today than when he wrote it and most modern style guides say that either relative pronoun can be used with restrictive clauses. For example, I found this sentence quoted approvingly as an example under the equivalent section in "Oxford English": A suitcase which has lost its handle is useless. The clause "which has lost its handle" is certainly restrictive. If you take it out, you are left with "A suitcase is useless", obviously a different meaning to that intended. So, according to Fowler's rule, the which ought to be that. Despite the shift in style, there remain some situations in which that is still regarded as preferable to which, though they're difficult to tie down. Here are some instances, but don't take them as a full list of cases, and they are tendencies, not full-blown rules: In clauses that follow impersonal constructions, such as it is, that is preferred: "It was the dog that died". Clauses which refer back to the words anything, nothing, something, or everything have a slight preference for that over which: "Can you think of anything that still has to be done?" Clauses which follow a superlative also tend to prefer that: "Thank you for the most superb dinner that I've ever eaten". In part, it seems probable that this preference is derived from stress and rhythm. The word that contains "soft" sounds and is usually unstressed, whilst which contains a "harder" initial sound and is easier to stress. Several writers note that that tends to be preferred in speech, which may be due to the comparative ease with which that is and similar phrases can be contracted, for example to that's, compared with the equivalent expressions using which. Though you can use which instead of that in restrictive clauses, you can't do so the other way round: non-restrictive clauses ought always to start with which. Also, you can't change the punctuation rules; it is particularly important to watch this point if you decide to use which in a restrictive clause, as otherwise your poor reader has no clue at all how you intend the sentence to be read. Here is a rather artificial example to make the point: The cup which he stepped on is in the bin. The cup, which he stepped on, is in the bin. In the first, you are being told about a specific cup with the special property that it is the one he stepped on; in the second, the fact that he stepped on it is an ancillary bit of information. My view is that punctuation is more important than choice of pronoun in such situations. You won't be thought wrong if you use that in the first case (and will avoid the thunder of pedants' condemnation) but you will be justly criticised if you leave out the commas in the second. A further point worth noting is that the opening pronoun in restrictive clauses is frequently left out, so that you can say "The cup he stepped on is in the bin". Again, you can't do this with non-restrictive clauses. If you wish to write naturally, don't fuss too much about the usage of that versus which. Obsessive correction (what has sarcastically been called a "which hunt") is best avoided. If your sense of the language is not strong enough to be sure of the right pronoun, use that for the restrictive cases and which for the others and you won't go wrong. For credit, see http://www.worldwidewords.org/articles/which.htm