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SAT English
SAT grammar: connect complete sentences correctly
A beginner-friendly guide to sentence boundaries, comma splices, semicolons, and the punctuation choices that show how ideas fit together.
SPSAT Practice Editorial6 min read
The short version
What you'll take away
- Find the subject and verb on both sides of a punctuation choice.
- A comma by itself cannot join two complete sentences.
- Choose punctuation based on whether the ideas are independent or connected.
In this article
Start by finding the complete thoughts
A complete sentence usually has a subject and a verb and expresses a complete thought. In “The team tested three designs,” team is the subject and tested is the verb. If a punctuation choice sits between two complete sentences, both sides need a valid connection.
On the SAT, punctuation options often look similar. Ignore which one seems most formal at first. Mark the subject and verb in each part, then decide whether each side could stand as its own sentence.
Know the common sentence connections
A period separates two complete sentences. A semicolon can join two closely related complete sentences. A comma plus a coordinating conjunction—such as “and,” “but,” or “so”—can also join them. A colon can follow a complete sentence to introduce an explanation or example.
A comma alone cannot join two complete sentences. That error is called a comma splice: “The sample was small, the results were promising.” Repair it with a period, a semicolon, or a comma and conjunction: “The sample was small, but the results were promising.”
See the skill
Same two complete thoughts, different joins
The sample was smallthe results were promising
- Period
. Creates two complete sentences.
- Semicolon
; Joins two closely related complete sentences.
- Comma + but
, but Joins the thoughts and signals contrast.
- Comma alone
, A comma by itself creates a comma splice.
- Complete sentence + period + complete sentence.
- Complete sentence + semicolon + closely related complete sentence.
- Complete sentence + comma + and/but/so + complete sentence.
- Complete sentence + colon + explanation or example.
Practice the two-side check
Sample: “The first trial produced mixed results ______ the second trial confirmed the pattern.” Both “the first trial produced mixed results” and “the second trial confirmed the pattern” are complete sentences. A semicolon works, as does “, but” if the intended relationship is contrast.
Now compare: “Researchers repeated the test ______ improving the measurement.” The words after the blank do not form a complete sentence, so a semicolon would be incorrect. The phrase explains why they repeated it; “to improve the measurement” fits without separating two sentences.
Your turn
Quick practice
Choose the punctuation that correctly joins these related complete sentences: “The first map was incomplete ______ the updated map included the entire coastline.”
Hint: Check whether the words before and after the blank can each stand as a sentence.
Sources & further reading
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