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What is a Sentence? Here’s What You Need to Know

sentence diagram


A sentence. Easy peasy, or so you might think. But when was the last time you thought about sentences? When have you wondered what, exactly, a sentence is?

“It’s a complete thought,” you might say, confidence oozing from your pores. Some of you cross your arms over your chest, roll your eyes, or even quit reading.

But wait. Stop. Do you really know what a sentence is?

And can you imagine why I’m bringing it up?

In the last week or so, I’ve seen so many similar punctuation problems in my editing work or articles I’ve read that I had to think about it. It’s like a disease going around, and I kept thinking if only the writer understood what a complete sentence is, the mistake wouldn’t be made. The rhythm of the writing wouldn’t be all wonky, and it would actually be pretty darned good. I’ve even seen the same problems on a site about copywriting. 

If you know exactly what a sentence must contain to be called a sentence, you’ll save yourself a lot of time and frustration with punctuation and grammar when things get complicated.

  • your readers won’t get confused, and your writing rhythm will be smoother.
  • business communication, including query letters, will be more successful.
  • your blog posts will be more professional and make you look good.
  • you might save money if you hire an editor, since many charge according to the level of work required.
  • you’ll know how to break the rules with confidence and style
  • you’ll be a stronger writer, and you might become a grammar or punctuation pro if you build on the knowledge.

Back to that complete thought business.

“A sentence is a complete thought” is what many of us were taught in high school and even college composition classes. But a sentence is not defined by whether it is or isn’t a complete thought. What the hell is a complete thought anyway? Creative people, especially, don’t always think in words (or in complete sentences); we think in pictures and images and the emotions or additional images they trigger.

“Oooh gorgeous!” is a complete thought. It’s something you might say when admiring a friend’s outfit, a photograph, or artwork. But it’s not a sentence.

“Oh, my God” or OMG is a complete thought that can mean a lot of things depending on the context. But that isn’t a sentence, either.

“Pffft” is a complete thought when uttered in disgust at a suggestion which you have no intention of following. Is it a sentence? Um, no. It’s not.

Let’s just toss that complete thought business out the window, shall we?

A sentence, also called an independent clause, contains a subject and a verb.

Thinking in terms of an “independent clause” instead of a complete thought will help because it has a specific meaning.

A clause is a group of words that contains a subject and a verb. A clause can be “dependent,” which means it’s not a complete sentence due to certain words or phrases it starts with. But we’re talking about “independent clauses” here—complete, correct sentences.

An independent clause contains both a subject and a verb (also called a predicate) and does nor include words that make it dependent.*

And that’s it. That is a sentence. Say it again, with feeling:

An independent clause contains both a subject and a verb and does not include words that make it dependent.*

Granted, what constitutes a subject or a verb can get tricky, and sometimes the subject is only implied. And any independent clause (complete sentence) can get so twisted or complicated we can hardly see what the subject is and the verb it’s connected to. But with practice, you’ll spot an independent clause—and the subject and verb—right away.

*Words that make a clause dependent (not an independent clause or complete sentence) often start with after, although, as, as if, because, before, even if, even though, if, in order to, since, though, unless, until, whatever, when, whenever, whether, and while. These are called “dependent markers” and alert you to a dependent clause (incomplete sentence).

Examples: Although she worked quickly. While the horse ran. Even though the house was painted white. None of these are independent clauses because, although they contain a subject and a verb, the dependent marker makes them dependent. 

Here’s what you need to know about sentences.

A subject is the main focus of the independent clause (complete sentence). It’s the actor of the sentence, the who or what, and it controls the verb tense. More on this below.

A verb is an action word or a being word, and it describes what the subject does (an action verb) or what it is (a linking verb that connects to a state-of-being word).

Here is a list of common action verbs.

Here is a list of linking verbs.

Helping or auxiliary verbs are used for changing verb tenses and adding meaning. These include forms of the verbs

  • To be: am, is, are, was, were, be, been.
  • To have: have, has, had.
  • To do: do, does, did.

The subject does the verb.

Here are some simple independent clauses (sentences) that contain a subject and a verb. Subjects and verbs are underlined.

The coffee cup is empty. (A linking verb, is, describes the cup’s state of being. The cup is not actually doing anything.)

The cup fell off the table. (Fell is an action verb.)

The tadpole grew legs. (Grew is an action verb.)

The horse is running. (Is running combines a helping verb with the present progressive tense of the verb to run.)

Please note: example sentences are intentionally simple. They are not meant to represent beautiful writing or literary genius.

Sometimes an independent clause (a sentence) has two or more verbs.

Two verbs mean the subject is doing two things or is being two or more things.

The coffee cup is empty and seems dirty. (two linking verbs)

The cup fell off the table and rolled under the chair. (two action verbs)

The tadpole grew legs and hopped. (two action verbs)

The horse ran and snorted happily. (two action verbs)

Sometimes an independent clause has two or more subjects.

The coffee cup and cereal bowl are empty. (linking verb)

The cup and bowl fell off the table. (action verb)

Tadpoles and starfish grow legs for different reasons. (action verb)

Horses and dogs love to play. (action verb)

A subject is usually a noun, but other words can work as a subject.

A noun is a person, place, thing, or idea (any sort of “thing” that will work with a verb). Here are some examples.

Common nouns such as a boy, girl, apples, bikes, queen, mountain, city, province, lake, or house can be subjects.

Proper nouns such as Juan, Karla, Queen Elizabeth, and Saskatchewan can be subjects. They are always capitalized.

Pronouns such as he, she, it, we, you (plural), and they can be subjects. These pronouns are called subjective pronouns because they can be subjects in a sentence. Objective pronouns like me, him, her, them, and us are never subjects.


A gerund is the -ing form of a verb that describes an action or state of being. It’s an -ing word (often used as a verb) that’s a thing. It can do a verb. 

Running, sleeping, skating, reading, cooking, riding, eating, and sailing are examples of gerunds.

Running is my favorite sport.

Reading remains her main hobby.

Cooking will be something we do together.

Sleeping provides time for the body to relax.

Horseback riding offers fun and exercise.

Sailing can do wonders for your health.

A gerund, when used as a subject, most often works with a form of the verb to be: is, was, were, will be, has been, would have been, and so on. But it’s also paired with to do and, in certain contexts, other verbs.

Infinitives (to+verb) can also act as subjects.

To swim in the ocean can be dangerous.

To drive here isn’t a good idea.

To err is human.

To see the morning sun makes my whole day brighter.

Implied subjects

In some independent clauses, the subject is left out because the reader will understand from context what it is. This usually involves imperative sentences (directives, commands, orders), and the subject is you.

(You) Stop!

(You) Watch where you’re going.

(You) Be careful with this.

(You) Don’t take your foot off the gas.

(You) Remember to feed the dog.

(You) Make a left here.

(You) Preheat the oven.

To recap what we’ve learned about sentences is my intention now.

  • An independent clause is a complete sentence.
  • Independent clauses contain both a subject and a verb and do not include words that make it dependent.
  • Any independent clause may contain more than one subject or more than one verb.
  • Nouns and pronouns are the most common subjects of sentences.
  • Other words can also function as subjects when paired with a verb.

Helpful Tip: Prepositions, adjectives, or adverbs are never the subject of a sentence.

And that’s what a complete sentence is. Stay tuned for more on verbs in a sentence, complicated situations, and how this applies to grammar and (especially) punctuation.

PS What’s the subject of the last sentence just above?

Editing Software for WritersPhoto credit: Photophilde “Running Horse”

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