The Relative Pronouns "That" and "Which"

First, I wish to thank PoeJoe for such an intriguing debate topic. I have learned much while researching it and I hope I can do it justice. Before I get into the meat of my argument I would like to help clear up some terms. In different sources clauses are referred to as "essential", "restrictive", or "defining", or their antithesis. The three terms are used interchangeably. === Pro's argument consists largely of anecdotal evidence; a few specific examples he found where the two words happen to be interchangeable or were used incorrectly. Unless Pro can present an authoritative and statically significant account of actual usage, I will ignore his examples as fallacious and address the parts of his argument that are more sound. (http://www.iep.utm.edu...) Regarding Pro's citation http://englishplus.com... -- A site set up to advertise a computer program is hardly authoritative, so this citation can be safely ignored. Regarding Pro's citation http://www.wsu.edu... -- Paul Brians is obviously a highly qualified expert on the English language and the fact that he doesn't see a distinction seems very damning. However Mr. Brians is talking about the general case and is being entirely too glib. In the cited source, Mr. Brians refers to a "small but impassioned group of authorities" but who are these people? I can't find them in my searches of authoritative sources. What do the authorities actually say (keeping in mind that Mr. Brians is one of them?) To find out, let's examine two of the most authoritative sources on the subject of English grammar. "The Little, Brown Handbook" (11th ed) and The OWL at Purdue (http://owl.english.purdue.edu...) both give us more detail than Mr. Brians has. What we find, when we actually examine the authoritative sources, is that the two words are interchangeable when referring to things in restrictive clauses, however they are not interchangeable when referring to things in non-restrictive clauses (where only "which" should be used,) nor are they interchangeable when referring to people (where only "that" or "who" should be used, but "which" should never be used.) Even in the cases where the two words are technically interchangeable, use of "which" is considered more formal, and there are several cases when "that" is more appropriate than, and is preferred to "which". Below are the cases where "that" and "which" are not interchangeable. The last one especially, I'm sure even Mr. Brians will agree with. 1) While it is the case that both "that" and "which" can be used in restrictive clauses, only the later can be used in non-restrictive clauses. ï¿½ï¿½ï¿½He made an iceberg Caesar salad, which didn't taste quite right. (correct) ï¿½ï¿½ï¿½He made an iceberg Caesar salad, that didn't taste quite right. (incorrect) 2) There are several cases when "that" is more appropriate than "which". ï¿½ï¿½ï¿½A) After pronouns that refer to quantities. ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½Every detail that you can remember will be helpful. (correct) ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½Every detail which you can remember will be helpful. (incorrect) ï¿½ï¿½ï¿½B) After verbs that answer the question "what?" ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½Mike says that you better get out of the shower. (correct) ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½Mike says which you better get out of the shower. (incorrect) ï¿½ï¿½ï¿½C) After a noun modified by a superlative adjective ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½He sat in the biggest chair that was in the house. (correct) ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½He sat in the biggest chair which was in the house. (incorrect) ï¿½ï¿½ï¿½D) After ordinal numbers ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½The first car that crossed the finish line was blue. (correct) ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½The first car which crossed the finish line was blue. (incorrect) ï¿½ï¿½ï¿½E) If the verb in the main clause is a form of "BE" ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½The living room was the one that the man died in. (correct) ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½The living room was the one which the man died in. (incorrect) 3) "That" can be used to refer to people, whereas "which" cannot. For example: ï¿½ï¿½ï¿½JD is the man that does the voice over on Scrubs. (correct) ï¿½ï¿½ï¿½JD is the man who does the voice over on Scrubs. (correct) ï¿½ï¿½ï¿½JD is the character which does the voice over on Scrubs. (incorrect)