My question pertains to general comma usage. My son's homework tonight consisted of combining two sentences using the conjunctions "and" or "but". His first two sentences were.... "The wind howled. The sand blew around" In their example, they combine the sentences like this-- "The wind howled, and the sand blew around. My question is simply, do you need the comma in this instance or is the conjunction by itself correct. What are the rules concerning comma usage? And if you leave out the "and" then wouldn't you just link these two thoughts with a semicolon?
Basically, you always need a comma to separate clauses, unless the sentence is so short that misreading would be impossible.

If I give you the start of a sentence:

"The wind howled and ..."

you don't know if there is another verb coming, or something else (like a clause). The comma helps to tell the reader: "That thought is finished and another is about to begin."

However, consider this sentence:

"He fought and he won"

The eye can take it in one pass, so a comma to separate the clauses would be superfluous (although it wouldn't be wrong). There is room for a range of styles from "puntuation heavy" to "punctuation light".