bedrooms." incorrect "The toys that are in the garden are not my children's." "The toys, that are in the garden, are not my children's." incorrect In the "incorrect" sentences, "which" is the right pronoun to use. There is yet another type of relative clause in which "which" is preferred to "that": what is called "sentential relative clause" by some authors because it does not modify any preceding nouns in particular but a whole clause: "John was late for dinner last night, which made me angry." In this sentence, "which" refers to/replaces the whole clause "John was late for dinner last night". Some teachers tell their students that a good way to recognise this use of "which" is to see if it can be replaced by "the fact": "John was late for dinner last night; 'the fact' made me angry." This thread confuses several different uses of the two words in its discussions. In your case: I know which is the better car -- the speaker knows but has not revealed the information. I know that is the better car -- this ' that ' is not a relative pronoun; it is a demonstrative pointing to the better car, so the information has been revealed. The same sentence can also be cast as: I know (that) that is the better car . *Usenet post removal: Use 'X-No-Archive' or please send proof of the poster's email, we will remove immediately. Views expressed in this community do not reflect the views of MediaCet