Grammar glossary: sentence

The word “sentence” is defined in various ways, but the way the word is generally used in traditional grammar has one specific meaning:  A sentence is a statement or question that consists, at least, of (1) a subject and (2) an accompanying verb that reflects time (past or non-past) or contains a modal auxiliary (e.g., “must,” “can,” “will,” etc.)*  Therefore, single words are not sentences, and phrases like “Not yet,” “In the kitchen,“ “Beautiful day!” and “To be or not to be” are not “sentences.”

Things like “Oh, no!” “Congratulations!”  and “Huh?” are certainly complete and important things to say as well, but they are not considered “sentences” as far as English grammar is concerned. That does not mean that there is anything wrong with them.  It’s just that they cannot be defined as “sentences.” Moreover, something like “my leaving on Friday” is not a sentence because, even though there is an action, “leaving,” and somebody doing that action (me), the verb form “leaving” does not show whether it refers to past or non-past time.  (“Friday” could refer either to last Friday or next Friday or some other Friday in the past or future.) “Leaving” is a timeless form, and a “sentence,” according to notions of grammar, must show past or non-past time in the verb (or contain a modal auxiliary). In addition, the word “my” in “my leaving on Friday” is a possessive adjective rather than a noun, so it can’t be considered a subject of a sentence. (Actually, this whole phrase “my leaving on Friday” could be the subject of a sentence because it is acting as a noun.)

A subject of a sentence must be a noun, or something that functions like a noun. For example, it may be a subject pronoun (such as “we,” “I,” “he,” “she”), a gerund, or a phrase that functions as a noun. Therefore, a string of words like “She walked” is a full sentence, but “her walking” is not. Similarly, “He helped” is a full sentence, but “him helping” is not.

It’s important to note that a subject of a sentence can be quite long. A subject can consist of one word or it can consist, for example, of one noun and many adjectives and adjectival clauses and phrases.  For example, the phrase “That friendly old guy at the party that asked me that question about my mother” can function as the subject of a sentence.  It is not in itself a sentence even though it is long and it has a verb, “asked,” which goes with “guy.”  It is not a sentence because the phrase “that asked me a question about my mother” is working as an adjective simply to describe which “guy” is being talked about.   The verb “asked” is a subordinate verb, not a main verb (a required verb to make a sentence) because it is part of this adjectival clause.  A full sentence would have to tell us what this friendly old guy at the party who asked me a question about my mother actually did.

*Imperative sentences, such as “Stay there!” “Put the keys on the table,” are considered complete grammatical sentences even though their intended subject, “you,” is not expressed.