What is a complete sentence?

Learning to write in complete sentences is a necessary skill. In order to fully understand the construction of a complete sentence, we need to define what a sentence actually is.

Sentences serve as a framework for people to clearly express their ideas in writing. There are several characteristics that must be met in order for a written thought to be considered a complete sentence. A complete sentence must: begin with a capital letter, end with a punctuation mark (period, question mark, or exclamation point), and contain at least one main clause. A main clause includes an independent subject and verb to express a complete thought.

As any English grammar teacher will tell you, a complete sentence has at least one main clause, or subject-verb pair. They’re a pair because they match. They match because, well, they work smoothly as a team. One half of the pair (the verb) expresses action or being, and the other half (the subject) is whatever or whoever does the action or exists in the state of being. Here are subject-verb pairs that match:

Eggworthy scrambled.

Ms. Drydock has repaired.

Just for comparison, here is one mismatch:

Eggworthy scrambling

When you’re texting or IMing (instant messaging), space is tight. Every character counts, including spaces. Therefore, many people opt for “sentences” that contain only verbs, when the meaning is clear. Check out this text: Went home. Fed cow. Cleaned barn.

Complete sentences may also include more than one subject-verb pair:

Dorothy fiddled while the orchestra pit burned. (Dorothy = subject of the verb fiddled, orchestra pit = subject of the verb burned)

Not only did George swim, but he also sipped the pool water. (George = subject of the verb did swim, he = subject of the verb sipped)

Complete sentences may also match one subject with more than one verb, and vice versa:

The lizard with a British accent appeared in three commercials but sang in only two. (lizard = subject of verbs appeared, sang)

Alice and Archie will fight endlessly over a single birdseed. (Alice, Archie = subjects of the verb will fight)

Complete sentences that give commands may match an understood subject (you) with the verb:

Visit Grandma, you little creep! (you-understood = subject of the verb visit)

What’s an incomplete sentence?

Simply put, an incomplete sentence is one that does not express a full thought (also referred to as sentence fragments which usually do not include both a subject and a verb). It’s the moment in the television show just before the last commercial. You know what I mean. The hero slowly edges the door open a few inches, peeks in, gasps, and . . . FADE TO DANCING DETERGENT BOTTLE. You were planning to change the channel, but instead you wait to see if the villain’s cobra is going to bite the hero’s nose. You haven’t gotten to the end, and you don’t know what’s happening.

A complete sentence is the opposite of that moment in a television show. You have gotten to the end, and you do know what’s happening. In other words, a complete sentence must express a complete thought.

Complete sentence examples and context

Check out these complete sentences. Notice how they express complete thoughts:

Despite Eggworthy’s fragile appearance, he proved to be a tough opponent.

I can’t imagine why anyone would want to ride on top of a Zamboni.

Did Lola apply for a job as a Zamboni driver?

For comparison, here are a few incomplete thoughts:

The reason I wanted a divorce was

Because I said so

Yes, in context those incomplete thoughts may indeed express a complete thought:

Sydney: So the topic of conversation was the Rangers’ season opener?

Alice: No! “The reason I wanted a divorce” was!

and

Sydney: Why do I have to do this dumb homework?

Alice: Because I said so.

Fair enough. You can pull a complete thought out of the examples. However, the context of a conversation is not enough to satisfy the complete thought/complete sentence rule. To be “legal,” your sentence must express a complete thought.

In deciding whether you have a complete sentence or not, you may be led astray by words that resemble questions. Consider these three words: who knits well. A complete thought? Maybe yes, maybe no. Suppose those three words form a question:

Who knits well?

This question is understandable and its thought is complete. Verdict: legal. Suppose these three words form a statement:

Who knits well.

Now they don’t make sense. This incomplete sentence needs more words to make a complete thought:

The honor of making Fido’s sweater will go to the person who knits well.