a non-restrictive relative clause is surrounded by pauses in speech and by commas in writing, whereas a restrictive clause is not. Compare the following sentences, which have quite different meanings and intonation, depending on whether the commas are inserted: (1) The builder, who erects very fine houses, will make a large profit. (non-restrictive) (2) The builder who erects very fine houses will make a large profit. (restrictive) The first expression refers to an individual builder (and it implies that we know, or know of, the builder, which is the referent). It says that he builds "very fine" houses, and that he will make a large profit. It conveys these meanings by deploying a non-restrictive relative clause and three short intonation curves, marked-off by commas. The second expression refers not to a single builder but to a certain category, also called a set, of builders who meet a particular qualification, or distinguishing property: the one explained by the restrictive relative clause. Now the sentence means: it is the builder who builds "very fine" houses who will make a large profit. It conveys this very different meaning by providing a restrictive relative clause and only one intonation curve, and no commas. Commas are, however, often used erroneously, probably because the rule is taught based on logic and most people are not aware that they can trust their ear in deciding whether to use a comma. (English uses commas in some other cases based on grammar, not prosody.) Thus, in speaking or writing English prose, a restrictive rather than non-restrictive meaning (or vice versa), requires the correct syntax by choosing the appropriate relative clause (i.e., restrictive or non-restrictive) and the appropriate intonation and punctuation. To determine whether a relative clause is restrictive or non-restrictive a simple test can be applied. If the basic meaning of the sentence (the thought) is not changed by removing the relative clause, the relative clause is not essential to the basic thought and is non-restrictive. Alternatively, if the essential meaning of the thought is disturbed, the relative clause is restrictive. Restrictive relative clauses are also called integrated relative clauses, defining relative clauses, or identifying relative clauses. Conversely, non-restrictive relative clauses are called supplementary, appositive, non-defining, or non-identifying relative clauses. Also, some integrated clauses may not be truly restrictive; see integrated clauses, and for more information see restrictiveness. Integrated clauses that are not restrictive Although the term "restrictive" has