A clause is a group of related words containing a subject and a verb A clause can be usefully distinguished from a phrase, which is a group of related words that does not contain a subject-verb relationship, such as "in the morning" or "running down the street" or "having grown used to this harassment." A review of the different kinds of phrases might be helpful.

Words We Use to Talk about Clauses

Learning the various terms used to define and classify clauses can be a vocabulary lesson in itself. This digital handout categorizes clauses into independent and dependent clauses. This simply means that some clauses can stand by themselves, as separate sentences, and some can't. Another term for dependent clause is subordinate clause: this means that the clause is subordinate to another element (the independent clause) and depends on that other element for its meaning. The subordinate clause is created by asubordinating conjunction or dependent word.

An independent clause, "She is older than her brother" (which could be its own sentence), can be turned into a dependent or subordinate clause when the same group of words begins with a dependent word (or a subordinating conjunction in this case): "Because she is older than her brother, she tells him what to do."

Clauses are also classified as restrictive and nonrestrictive clauses. (The words essential and nonessential are sometimes used and mean the same thing as restrictive and nonrestrictive, respectively. British grammarians will make this same distinction by referring to clauses with the terms defining and non-defining.) A nonrestrictive clause is not essential to the meaning of the sentence; it can be removed from the sentence without changing its basic meaning. Nonrestrictive clauses are often set apart from the rest of the sentence by a comma or a pair of commas (if it's in the middle of a sentence).

• Professor Villa, who used to be a secretary for the President, can type 132 words a minute.

Review the Notorious Confusables section on the difference between That and Which for additional clarification on the distinction between restrictive and nonrestrictive.

Relative clauses are dependent clauses introduced by a Relative Pronoun (that, which, whichever, who, whoever, whom, whomever, whose, and of which). Relative clauses can be either restrictive or nonrestrictive. Review the section on Comma Usage for additional help in determining whether relative clauses are restrictive or nonrestrictive (parenthetical or not) and whether commas should be used to set them off from the rest of the sentence. In a relative clause, the relative pronoun is the subject of the verb (remember that all clauses contain a subject-verb relationship) and refers to (relates to) something preceding the clause.

• Giuseppe said that the plantar wart, which had been bothering him for years, had to be removed.

(In this sentence, the clause in this color is a restrictive [essential] clause [a noun clause — see below] and will not be set off by a comma; the underlined relative clause [modifying "wart"] is nonrestrictive [nonessential — it can be removed from the sentence without changing the meaning of the sentence] and is set off by commas.)

Some relative clauses will refer to more than a single word in the preceding text; they can modify an entire clause or even a series of clauses.

• Charlie didn't get the job in administration, which really surprised his friends.
  Charlie didn't get the job in administration, and he didn't even apply for the Dean's position, which really surprised his friends.

A relative clause that refers to or modifies entire clauses in this manner is called a sentential clause. Sometimes the "which" of a sentential clause will get tucked into the clause as the determiner of a noun:

• Charlie might very well take a job as headmaster, in which case the school might as well close down.

Finally, everybody's favorite clause is the Santa Clause, which needs no further definition.