Comma Usage with Introductory Phrases
Know when an introductory word, phrase, or clause needs a comma before the main sentence begins.
Introduction
A large share of SAT Writing punctuation questions test one rule: whether a comma is needed after an introductory element, before the main clause of the sentence starts.
Theory
An introductory element — a word (However,), a phrase (Having finished the marathon), or a dependent clause (Although it was raining) — sets up the main clause that follows. It should almost always be followed by a comma so the reader knows where the "setup" ends and the main sentence begins.
The main clause is the part that could stand alone as a complete sentence. If you can identify where that complete sentence starts, the comma goes right before it.
Examples
Example: "Having finished the marathon, Maria felt an overwhelming sense of relief." The introductory phrase is "Having finished the marathon." The main clause — "Maria felt an overwhelming sense of relief" — could stand alone, so the comma goes right before it.
Exception: very short introductory words (like "Then" or "Now") at the start of a short sentence sometimes read fine without a comma, but the SAT virtually always tests the clear-cut, comma-required case.
Practice
Check your understanding 1
Choose the correctly punctuated sentence.
Check your understanding 2
Choose the correctly punctuated sentence.
Common mistakes
Forgetting the comma entirely after a long introductory phrase, or — the opposite error — adding a comma that splits the introductory phrase itself into two pieces (e.g. "Having, finished the marathon...").
Where to go next
Practise this: drills for this topic in the question bank.