SAT Sentence Boundaries Rules
By the Cheetah Prep team
The most tested idea in the entire section is where one sentence stops and the next begins. Two complete sentences cannot hold hands with just a comma. That is a comma splice, and it is wrong every time. To join them you need a period, a semicolon, or a comma plus one of the FANBOYS words: for, and, nor, but, or, yet, so.
The move the SAT pulls is offering the same split four ways and asking which punctuation is right. So the real skill is telling an independent clause, which can stand alone, from a dependent one, which starts with a word like because, although, or when and cannot. Read that correctly and the punctuation follows on its own.
The Sentence Boundaries Rules the SAT Tests
Two independent clauses need real punctuation
Two complete sentences cannot be joined by a comma alone. Use a period, a semicolon, or a comma plus a FANBOYS conjunction.
The experiment failed, the team ran it again the next morning.
The experiment failed, so the team ran it again the next morning.
On the SAT: The most tested grammar concept on the section. The SAT offers the same clause split with a comma, a semicolon, a period, and a dash, and only one is punctuated correctly.
A fragment is missing a subject or a verb
Every sentence needs a subject and a working verb. A phrase or a dependent clause on its own is a fragment.
Because the bridge, built in 1932, still carrying traffic today.
The bridge, built in 1932, still carries traffic today.
On the SAT: Answer choices sometimes strip the main verb or bury it in an -ing form, leaving no complete sentence.
A dependent clause can attach to an independent one
A dependent clause (starting with words like because, although, when, since) joins an independent clause with just a comma, or with no comma if it comes second.
Although the data was clear; the committee wanted a second study.
Although the data was clear, the committee wanted a second study.
On the SAT: The SAT tests whether you can tell a dependent clause from an independent one, since only two independent clauses need heavy punctuation.
Drill Sentence Boundaries on Real Questions
Knowing a rule and spotting it under time pressure are different skills. The diagnostic shows whether sentence boundaries is costing you points, and Cheetah Prep drills each rule in real digital SAT questions until you catch the pattern on sight.
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