13.3.8.2 Use a comma after introductory elements that are long, have verbs in them, or could be misread without the comma
Should you use a comma after a group of words introducing the main idea of a sentence? Here are five defining sentences:
- On Tuesday he came to see me.
If the introductory words are short and are simple and contain no verb form, do not separate them from the main idea--the independent clause--that follows.
- When it was Tuesday, he came to see me.
If the introductory group of words has a subject and verb but cannot stand alone as sentence, use a comma. Such clauses generally start with when, while, because, as, since, if, although, though, before, or after.
- Remembering me, he came to see me.
If the introductory group of words contains a word ending in "-ed" or "-ing" and is not acting as the subject of the independent clause, use a comma. Such introductory groups of words are called participial phrases.
- After many hours of thought and hours of fruitless fretting, he came to see me.
If the introductory group of words is substantial, use a comma. What is substantial? Four words or more.
- Inside, the diners were enjoying their meals.
If a comma would prevent misreading, use one.
So the rule could roughly be reduced to this: if the introductory element is long or has a verb form in it or if a comma would prevent misreading, use a comma to separate the element from the main idea which follows.
==>Guidelines ==>Conventions
==>Problems ==>Commas