ACT and SAT Punctuation 101: Complete and Incomplete Sentences

Bonus Material: PrepMaven’s Identifying Complete and Incomplete Sentences Worksheet

Punctuation is the most heavily tested English grammar concept on the ACT and SAT. The good news is that ACT and SAT punctuation rules are limited. 

In fact, understanding SAT and ACT punctuation largely has to do with one skill: knowing how to identify complete and incomplete sentences.

This post will teach you how to identify complete and incomplete sentences in any context. 

We strongly encourage students to read this post before learning the punctuation for combining these sentences.

You’ll also get access to our free Complete and Incomplete Sentences worksheet, which includes additional practice questions. Grab it below before we get started.

Here’s what we cover in this post:


ACT and SAT Punctuation Questions: Where You’ll See Them

As we’ve discussed in other posts, the ACT and SAT are very different tests. All U.S. colleges and universities accept either ACT scores or SAT scores from applicants, without preference.

That being said, we encourage our students to prep for the test that’s most likely to give them their highest score. If you’re unsure which test is best for you, ask yourself these five questions now.

Punctuation Questions on the ACT and SAT

Regardless of which test is right for you, you’ll definitely need to know how to use certain kinds of punctuation in various contexts. You’ll find punctuation questions on these sections of each test:

  • ACT English
  • SAT Writing & Language

However, knowledge of appropriate punctuation can be helpful on the optional essay portion of either test.

Essay readers are interested in your ability to connect ideas logically on the page and use standard English conventions appropriately. Effective punctuation usage can definitely help you closer to a higher essay score.

How many punctuation questions can you expect to see on the ACT and the SAT?

Based on our analysis of officially released ACT and SAT practice tests, we’ve crafted a breakdown here:

Punctuation Questions on the ACT Punctuation Questions on the SAT
12-16 5-7

Remember that the ACT English section is longer than SAT Writing & Language, with 75 questions (as opposed to 44 questions). Get insight into the way these tests are structured in our ACT Format and The 5 SAT Sections: What You Need to Know posts.

How will you know that you’re encountering an ACT or SAT punctuation question? Easy!

You’ll typically see different kinds of punctuation in the answer choices. At the very least, you’ll generally see punctuation (like commas) in different places in the selected word or phrase.

Here’s a sample punctuation question from an SAT Writing & Language section:

SAT Punctuation Question
Source: College Board Official SAT Practice Test 1

Notice how the answer choices to this question include a semicolon, colon, and various commas. That’s a sure sign that you’re dealing with an SAT punctuation question!


Complete Sentences in a Nutshell

Remember: the list of punctuation rules you need to know for the SAT or ACT is finite. Before we can get to that list, however, it’s important to understand complete and incomplete sentences.

Let’s start with complete sentences, as these are often easier for students to recognize.

Complete sentences are technically called independent clauses, but we’ll do our best to keep grammar jargon out of this post.

A complete sentence must have the following three things:

  1. Subject
  2. Verb
  3. The complete expression of an idea

A subject is a person, place, thing, or idea. Examples of subjects include apple, optometrist, dyslexia, and the United Kingdom. A verb expresses the action of a subject, such as iscompletedrunning, and have.

ACT and SAT Punctuation_ Complete Sentences

Now, what do we mean by “the complete expression of an idea”? Basically, this stipulates that the sentence doesn’t leave you hanging. It expresses a full idea.

Here’s an example of a complete sentence that expresses a full idea:

Cherise decided to travel to the United Kingdom and seek employment after she completed her teaching certification.

The subject of this sentence is “Cherise,” while the verb is “decided.” The sentence fully expresses the idea that Cherise made a choice to travel to another country following completion of her teaching certification.

Yet a sentence doesn’t have to be super long to express a full idea. Check out these sentences that are, in fact, complete:

I understand.

She couldn’t go.

David waited.

This discussion of complete sentences is best paired with one about incomplete sentences. We’ll talk about those now.


Incomplete Sentences in a Nutshell

Basically, if a sentence lacks one or more of the following things, it’s an incomplete sentence (or dependent clause):

  1. Subject
  2. Verb
  3. The complete expression of an idea

Here’s an example of a trademark incomplete sentence:

Although I intended to take the ACT twice

Notice how this sentence still has a subject (“I”) and a verb (“intended”). However, the sentence does not express a full idea. In fact, it leaves us hanging! We know this person intended to take the ACT twice, but the rest of the story is missing.

That word “although” is the secret culprit behind the incompleteness of this sentence. Subordinate conjunctions like although always make a sentence incomplete!

Here’s a list of common subordinate conjunctions. When you see these words at the start of a sentence on the ACT or SAT, be on the lookout for an incomplete idea:

while after because although before
unless as if since when
whenever whereas even though rather than until

Here are additional examples of incomplete sentences:

The long-awaited decision to appeal

While the rest of the class worked on the exam

Horses running through the field on a cloudy day


Identifying Complete and Incomplete Sentences

On the SAT and ACT, it can be challenging to identify complete and incomplete sentences.

Both ACT English and SAT Writing & Language contain dense, boring passages full of detailed sentences. It can be hard to wade through this extra verbiage and determine what kind of sentence you’re dealing with!

That’s why we encourage students to keep these tips in mind when dealing with ACT and SAT punctuation questions:

  1. Read the full context
  2. Focus on one idea or sentence at a time
  3. Look for the 3 components of a complete sentence
  4. Write down whether it’s incomplete or complete

Let’s apply these tips to a sample punctuation question now from an officially released SAT practice test:

Complete Sentences

Read the full context

It’s always essential to read the full context on any ACT English or SAT Writing & Language question. That means reading the full sentence expressed here, starting with “But Jason Box” and ending with “problem.”

Focus on one idea or sentence at a time

In this question, we can see that the punctuation in the answer choices separates two thoughts: “But Jason Box, an associate professor of geology at Ohio State, believes that another factor added to the early thaw” and “the “dark snow” problem.”

Incomplete and Complete Sentences_SAT

Let’s focus on one of these ideas at a time, to make things easy.

Look for the 3 components of a complete sentence

In analyzing “the “dark snow” problem,” we find a subject (problem) but no verb or complete expression of an idea. This is an incomplete sentence!

If we take a look at “But Jason Box, an associate professor of geology at Ohio State, believes that another factor added to the early thaw” we find a subject (Jason Box), a verb (believes), and a complete expression of an idea. This is a complete sentence!

Write down whether it’s incomplete or complete

You can do this by writing an “I” or a “C” above the relevant sentences.

Incomplete and Complete Sentences_SAT


Download PrepMaven’s Complete & Incomplete Sentences Worksheet

Remember: most punctuation questions on the ACT/SAT come down to your ability to distinguish complete and incomplete sentences. 

Students should thus boost their fluency in identifying these sentences before they start learning the punctuation rules for combining these sentences.

You can do exactly this with our free Complete and Incomplete Sentences worksheet.

Complete and Incomplete Sentences on the SAT:ACT

With this worksheet, you’ll get: 

  • A recap of what we discussed in this post
  • Guided examples of punctuation questions from official practice tests
  • 20+ practice questions that test your ability to identify complete and incomplete sentences
  • Detailed answers/explanations 


Kate_Princeton Tutoring_AuthorBioKate M.

Kate is a graduate of Princeton University (B.A. in English Literature and Interdisciplinary Humanities) and Boston University (M.F.A in Creative Writing). Over the last decade, Kate has successfully mentored hundreds of students in all aspects of the college admissions process, including the SAT, ACT, and college application essay.