At its most basic level, a sentence is a sequence of words that conveys a complete thought. This is formed by a subject (what the sentence is about, generally the noun or pronoun that is the focus of the action in a sentence) and a predicate (the verb plus any other information). The rule outlining the components of a sentence is: Subject + Predicate = Sentence.

Subjects

The subject of a sentence is the sentence topic (what a sentence is about). Subjects come in five varieties

1. nouns

2. pronouns

3. noun clauses

4. infinitives

5. gerunds

Nouns

Nouns are people, places, ideas, concepts, and things. Sentences can have multiple nouns, but the subject noun is the focus of the sentence. Essentially, it is the“star” of a sentence.

Example: Islam is a world religion.

Islam, world, and religion are all nouns, though only Islam is the subject of this sentence.

Pronouns

A pronoun takes the place of a noun to simplify a sentence. Pronouns include words like he, she, it, I, we, you, they, one, her, him, and them.

Example: Thomas was late for class because he overslept.

Noun clauses

A noun clause is a group of words that acts as a noun. When used as the subject of a sentence, a noun clause usually begins with one of the following words: that, how, when, what, where, why, and whether.

Examples:
What the researcher said was controversial.
That the research was controversial is an understatement.

Note that the noun clause is followed by a verb, which completes the sentence.

Infinitives

An infinitive is the to form of a verb. This basic form of a verb can be used as a noun. Thus, infinitives may also be subjects of sentences.

Example: To study is to be diligent.

Gerunds

A gerund is the -ing form of a verb, which may also be used as a subject. Like infinitives, gerunds used as nouns can be the subject of a sentence.

Example: Fencing became a popular sport in fifteenth century Spain.

Predicates

Predicates contain a verb, as well as any additional information used to describe a situation.

Examples:
This particular species thrives.
This particular species thrives in temperate, deciduous forests.

The predicate in each example completes the sentence. The first example contains only a verb (thrives), and the second example contains a verb and additional information (where the species thrives).

Imperative voice

The one (and only) exception to the rule

The rule ‘a subject + a predicate = a sentence’ has one exception: sentences in the imperative voice do not require subjects.

Example: State your name for the record.

In the imperative voice (commands), the subject is hidden because it is implied within the

predicate. (The subject you is implied in the example above.)