Reading & Writing · Standard English Conventions (~26% of RW)
Sentence Boundaries & Punctuation Rules
Key SAT Rule at a Glance
A comma splice occurs when two independent clauses (complete thoughts that could stand alone as separate sentences) are joined with only a comma. On the SAT, a comma splice is always grammatically incorrect. You can only connect two independent clauses with: (1) a period, (2) a semicolon, (3) a comma + FANBOYS conjunction (for, and, nor, but, or, yet, so), or (4) a colon/dash when the second clause illustrates the first.
1. The Four Legal Ways to Connect Independent Clauses
Every sentence boundary question on the Digital SAT boils down to identifying whether the clause before the punctuation and the clause after the punctuation can each stand alone as an Independent Clause (IC). When both sides are independent, only four punctuation patterns are permissible:
Period (IC. IC.)
Separates the two independent thoughts into two distinct sentences.
The experiment concluded yesterday. The team published its findings.Semicolon (IC; IC.)
Connects closely related independent clauses without a conjunction.
The experiment concluded yesterday; the team published its findings.Comma + FANBOYS (IC, and IC)
Requires both the comma AND one of the 7 coordinating conjunctions (For, And, Nor, But, Or, Yet, So).
The experiment concluded yesterday, and the team published its findings.Colon or Dash (IC : IC)
Must have a full independent clause before the colon; the clause after explains, specifies, or lists.
The experiment yielded one clear conclusion: the hypothesis was correct.Words like however, therefore, consequently, moreover, indeed, and furthermore are adverbs, NOT conjunctions. You cannot connect two independent clauses with a comma and however:
❌ The survey ended, however, the results were lost. (Comma splice!)
✓ The survey ended; however, the results were lost. (Correct semicolon + adverb)
2. Worked SAT Practice Question
The northern flying squirrel relies on subcutaneous membranes extending between its wrists and ankles to glide through dense forest __________ these flaps of skin generate sufficient aerodynamic lift to allow controlled glides exceeding fifty meters.
View Step-by-Step Explanation
Correct Answer: B (canopies; indeed,)
Clause 1 ("The northern flying squirrel relies on subcutaneous membranes...") is a complete independent clause. Clause 2 ("these flaps of skin generate sufficient aerodynamic lift...") is also a complete independent clause. Connecting them with only a comma (choices A and D) produces an illegal comma splice. Omitting punctuation entirely (choice C) creates a run-on sentence. Choice B correctly uses a semicolon to separate the two independent clauses, followed by the transitional adverb "indeed," set off by a comma.