| #2 (permalink) Sun Sep 03, 2006 10:50 am It should be 'the boxes THAT were sent to you last month...
While which (preceded by a comma) is used only to introduce nonrestrictive clauses, restrictive clauses can be introduced by either that or which.
The American Heritage Dictionary has this to say in its Usage Notes:
The standard rule requires that that should be used only to introduce a restrictive (or defining) relative clause, which identifies the entity being talked about; in this use it should never be preceded by a comma. Thus, in the sentence The house that Jack built has been torn down, the clause that Jack built is a restrictive clause identifying the specific house that was torn down. Similarly, in I am looking for a book that is easy to read, the restrictive clause that is easy to read tells what kind of book is desired. A related rule stipulates that which should be used with nonrestrictive (or nondefining) clauses, which give additional information about an entity that has already been identified in the context; in this use, which is always preceded by a comma. Thus, we say The students in Chemistry 101 have been complaining about the textbook, which (not that) is hard to follow. The clause which is hard to follow is nonrestrictive in that it does not indicate which text is being complained about; even if the clause were omitted, we would know that the phrase the textbook refers to the text in Chemistry 101. •Some grammarians extend the rule and insist that, just as that should be used only in restrictive clauses, which should be used only in nonrestrictive clauses. Thus, they suggest that we should avoid sentences such as I need a book which will tell me all about city gardening, where the restrictive clause which will tell me all about city gardening indicates which sort of book is needed. But this extension of the rule is far from universally accepted, and the use of which with restrictive clauses is common. Furthermore, since that cannot be used with clauses introduced by a preposition (whether or not restrictive), which is used with both clauses when such a clause is joined by and or or to another that does not begin with a preposition, as in It is a philosophy in which the common man may find solace and which many have found reason to praise.
And the Columbia Guide comments:
Many have thought it would be good were that always to be used to introduce only restrictive clause modifiers (The big dog that is barking is a nuisance) and which, only nonrestrictive ones (The big dog, which is barking, is mine). This neat dichotomy has been much recommended, and some conservative watchdogs of our Edited English do follow it pretty generally. But—especially in Conversational or Informal contexts—most of us use which almost interchangeably with that in restrictive modifiers and rarely but sometimes use that to introduce nonrestrictive modifiers. Then too we often omit any relative at all, as in the car I want to own, rather than the car that I want to own or the car, which I keep in the garage. Best advice: use that or which or nothing, depending on what your ear tells you. Then, when writing for certain publications, know that you may have to replace a good many whiches with thats, and perhaps a that or two with a which, to conform to the “rule” almost no one follows perfectly in other than Edited English and few can follow perfectly even there.
Native English teacher at Mister Micawber's
Joined: 17 Jul 2005