Dependent clause

A dependent clause, also known as a subordinate clause, subclause or embedded clause, is a certain type of clause that juxtaposes an independent clause within a complex sentence. For instance, in the sentence "I know Bette is a dolphin", the clause "Bette is a dolphin" occurs as the complement of the verb "know" rather than as a freestanding sentence. Subtypes of dependent clauses include content clauses, relative clauses, adverbial clauses, and clauses that complement an independent clause in the subjunctive mood.

Types

Content clause

A content clause, also known as a "noun clause", provides content implied or commented upon by its main clause. It can be a subject, predicate nominative, direct object, appositive, indirect object, or object of the preposition. Some of the English words that introduce content clauses are that, who, whoever, whether, why, what, how, when, and where. Notice that some of these words also introduce relative and adverbial clauses. A clause is a content clause if a pronoun could be substituted for it.
Examples:

I know who said that.
Whoever made that assertion is wrong.

In English, in some instances the subordinator that can be omitted.
Example 1:

I know that he is here.
I know he is here.

Example 2:

I think that it is pretty.
I think it is pretty.

Relative (adjectival) clause

In Indo-European languages, a relative clause, also called an adjectival clause or an adjective clause, meets three requirements:

Like all dependent clauses, it contains a verb. However, in a pro-drop language the subject may be a zero pronoun: the pronoun may not be explicitly included because its identity is conveyed by a verbal inflection.
It begins with a relative adverb or a relative pronoun . However, the English relative pronoun may be omitted and only implied if it plays the role of the object of the verb or object of a preposition in a restrictive clause; for example, He is the boy I saw is equivalent to He is the boy whom I saw, and I saw the boy you are talking about is equivalent to the more formal I saw the boy about whom you are talking.
The relative clause functions as an adjective, answering questions such as "what kind?", "how many?" or "which one?"

The adjective clause in English will follow one of these patterns:

Relative Pronoun + Subject + Verb
Relative Pronoun + Subject + Verb
Relative Adverb + Subject + Verb
Relative Pronoun + Verb
Relative Pronoun + Subject + Verb + Preposition
Preposition + Relative Pronoun + Subject + Verb
Possessive Relative Pronoun + Noun + Verb
Possessive Relative Pronoun + Noun + Subject + Verb

For a discussion of adjective clauses in languages other than English, see Relative clause#Examples.

Punctuation

English punctuation

The punctuation of an adjective clause depends on whether it is essential or nonessential and uses commas accordingly. Essential clauses are not set off with commas; nonessential clauses are. An adjective clause is essential if the information it contains is necessary to the meaning of the sentence:

The vegetables that people often leave uneaten are usually the most nutritious.

The word "vegetables" is non-specific. Accordingly, for the reader to know which are being mentioned, one must have the information provided in the adjective clause. Because it restricts the meaning of "vegetable", the adjective clause is called a restrictive clause. It is essential to the meaning of the main clause and uses no commas.
However, if the additional information does not help to identify more narrowly the identity of the noun antecedent but rather simply provides further information about it, the adjective clause is nonrestrictive and so requires commas to separate it from the rest of the sentence:

Broccoli, which people often leave uneaten, is very nutritious.

Depending on context, a particular noun could be modified by either a restrictive or nonrestrictive adjective clause. For example, while "broccoli" is modified nonrestrictively in the preceding sentence, it is modified restrictively in the following.

The broccoli which people leave uneaten is often nutritious.

Adverbial clause

"He saw Mary when he was in New York" and "They studied hard because they had a test" both contain adverbial clauses. Adverbial clauses express when, why, where, opposition, and conditions, and, as with all dependent clauses, they cannot stand alone. For example, When he was in New York is not a complete sentence; it needs to be completed by an independent clause, as in:

He went to the Guggenheim Museum when he was in New York.

or equivalently

When he was in New York, he went to the Guggenheim Museum.

Non-finite dependent clauses

Dependent clauses may be headed by an infinitive, gerund, or other non-finite verb form, which in linguistics is called deranked. For instance:

Sit up straight while singing.

In these cases, the subject of the dependent clause may take a non-nominative form. An example is:

I want ''him to vanish.''

Sentence structure

A complex sentence contains an independent clause and at least one dependent clause. A sentence with two or more independent clauses plus dependent clauses is referred to as a compound-complex sentence. Here are some English examples:
My sister cried because she scraped her knee.

Subjects: My sister, she
Predicates: cried, scraped her knee
Subordinating conjunction: because

When they told me '' I won the contest'', I cried, but I didn't faint.

Subjects: they, I, I, I
Predicates: told me, won the contest, cried, didn't faint
Subordinating conjunctions: when, that
Coordinating conjunction: but

This sentence contains two dependent clauses: "When they told me", and " I won the contest", the latter which serves as the object of the verb "told". The connecting word "that", if not explicitly included, is understood to implicitly precede "I won" and in either case functions as a subordinating conjunction. This sentence also includes two independent clauses, "I cried" and "I didn't faint", connected by the coordinating conjunction "but". The first dependent clause, together with its object, adverbially modifies the verbs of both main clauses.