On the ACT/SAT, the most common use of the semicolon is to separate two full and closely related sentences.

If you can already tell whether you’re looking at a full sentence, this rule will be straightforward for you. If you’re unsure, though, I recommend you check out my [article on full sentences versus fragments] before you continue.

Now, let’s turn our attention to the part of the rule about the sentences being closely related. This could mean that the sentences go “hand in hand” or that one leads logically into the next. Here are a few examples:

• Sam is saving the other half of his meatball hero; he wants to have it for dinner later.
• Please ensure your order is correct; no refunds will be issued after this point.
• Statistically, dogs are the most popular pet in the US; cats, however, are not far behind.
• People study foreign languages for different reasons; common motives include an interest in travel and access to more job opportunities.    

In the above examples, we can say that the sentences are closely related because the second one explains or elaborates on the first. There is a clear relationship between the sentences, and the semicolon is there to emphasize that.

However, we could also change the above semicolons to periods — and that would be equally acceptable. Some writers like using semicolons because they think they look sophisticated. Others prefer to stick to periods because they’re a punctuation mark that everyone understands. Bottom line: neither punctuation mark is “more correct” — it’s a matter of style.

On the ACT/SAT, a technique you can use is to try plugging in periods where there are semicolons (and vice versa). If you’re truly dealing with two full sentences, either punctuation mark should work.

Here’s another tip for the ACT/SAT: because both answer choices would be equally valid, you’ll never have to decide between one that has a period between full sentences and one that has a semicolon between full sentences.

There’s a caveat, though: if you seem to be dealing with answer choices that require you to pick between periods and semicolons, you’re probably dealing with a complex list — the one other use for semicolons you’ll need to know if you’re taking the SAT. (Complex lists are not typically tested on the ACT.) For more information on this topic, check out my article on [semicolon rule 2: separating the items in a complex list].

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