Here are the relevant bits from Mary-Clair Van Leunen's book "A Handbook for Scholars" (Knopf, 1978) on the topic of "Which-Hunting." (pgs. 135-137) ------------ Which Hunting I understand that if you tape-record a person who's carrying on a normal conversation, he follows the normal English pattern for relative pronouns, "that" for restrictive clauses, "which" for non-restrictive. He does, that is, unless you tell him that he's addressing an audience, or dictating a formal letter or a paper. At that point, he starts substituting "which" for "that." This is another of those bending-over-backwards errors, the ones that result from affecting an unnatural, prissy diction in writing. The first cure, then, is to listen to what you write. For many people that will be sufficient. * The novel which is emerging in the Third World does not fit our standard categories. If you're lucky, that will sound awful to you, and you'll change it easily and automatically to: The novel that is emerging in the Third World does not fit our standard categories. Don't give up if you can't hear it right away. Your ear has undoubtedly been battered by all the bad prose you've had to read, but the damage is not permanent. If you have a good grasp of comma punctuation, all you need to know is that which-clauses are set off by commas. These regulations, which Elizabeth had no intention of following, went into effect the following summer. No commas, no "which": * He prefered the settlement which his sister had proposed. He prefered the settlement that his sister had proposed. But if you're weak on both "which/that" and commas, you'll have to think about the grammar of restrictive and non-restrictive clauses. Restrictive clauses ("that" with no commas) are essential, defining, irremovable. Non-restrictive clauses ("which" with commas) are parenthetical, descriptive, detachable. The trouble comes in deciding what you mean to say. In most cases, you can't decide the sentence by itself; you need to look around at the context. The leaf ------- the grub has used for shelter now becomes its food. "That" with no commas or "which" with commas? There's no way to tell by looking at the sentence in isolation. Check the context to see how the clasues relates to the noun it's modifying. if "the leaf" is a fresh expression, not mentioned before, or not sufficient in itself for your reader to know what leaf you're talking about, the clause is restrictive. The leaf that the grub has used for shelter now becomes its food. If you've already talked about the leaf, your reader knows full well what leaf you mean, and you're just reminding him, the clause is non-restrictive. The leaf, which the grub has used for shelter, now becomes its food. Another way of checking the same distinction is to try out imaginary uprooting. The training ---- the Agency gives is free except for books and supplies. "That" with no commas or "which" with commas? Again, only the context can answer the question. But try ripping out the clause and putting it after the sentence. The training, which the Agency gives, is free except for books and supplies. But if the uprooted version is nonsense -- if the reader must ask, "What training? What are you talking about?" -- then the clause is restrictive. A restrictive clause uprooted would have to go before the sentence. The Agency gives training. The training is free except for books and supplies. If this is the only version that makes sense in context, what you want is "that" with no commas: The training that the Agency gives is free except for books and supplies. As a desperate last measure, if you're completely at a loss, use "that" with no commas. It's the more common construction by maybe ten to one, so the odds will be with you.