This is one of the most common errors involving commas on the ACT, and it’s one that’s very easy to identify and fix.
A compound item is simply two nouns or verbs joined by the word “and.” The rule is that you never need a comma before the “and.”
If the grammatical terminology makes you too nervous, there’s also a great shortcut: comma + and = period, and if you plug in a period, you won’t have two full sentences. Since the period isn’t correct, “comma + and” isn’t correct either.
Compound Subject Errors
Incorrect: The cover, and the binding of the old book are beginning to disintegrate.
Period replaces “comma + and:” The cover. The binding of the old book are beginning to disintegrate.
Correct: The cover and the binding of the old book are beginning to disintegrate.
Compound Object Errors
Incorrect: The book has many pages, and illustrations.
Period replaces “comma + and:” The book has many pages. Illustrations.
Correct: The book has many pages and illustrations.
Compound Verb
Incorrect: The cover of the old book is beginning to fade, and disintegrate.
Period replaces “comma + and:” The cover of the old book is beginning to fade. Disintegrate.
Correct: The cover of the old book is beginning to fade and disintegrate.
I have a follow-up more detailed question. What about a sentence like this:
Suzy loved to play outside because she could climbs trees or she could swing on the swing sets. (I made this a VERY simple sentence, but I’m dealing with more complex cases).
Is there a comma before OR because what follows could be a stand alone sentence? Or is there not, because both clauses following “because” are really explanations for the initial sentence?