Punctuation questions are at the heart of the ACT English section. If you know what you're doing, they are quite straightforward. But they are full of traps, ready to catch the inattentive student. So it's a good thing to know where these traps are set most frequently.
The two most common traps are: 1. comma separating the subject and verb; 2. comma in front of a prepositional phrase.
Commas are meant to separate clauses or items in a list, so commas are totally meaningless in the two places above: subject and verb are the heart of any clause, so don't separate them; prepositional phrases can cluster without any punctuation since they don't affect the number of clauses - they just make clauses bigger and add information.
An example for trap number one would be: He, went home. 'He' is the subject doing the verb 'went'. This duo is at the heart of any clause. The two should never be separated.
An example for trap number two would be: He went, to school. The prepositional phrase 'to school' does not alter the number of clauses; it is an extension of the clause started by 'he went'.
This is by far the most common trap in the ACT English section. So watch out, and don't get tempted to put in a comma before such a phrase even if it reflects a pause you would make when speaking.
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