Three marks cause the tricky errors: the colon, the semicolon and paired commas or dashes. Each has one test.
When to use it
Choices differ only by a colon, semicolon, comma, dash or no mark.
The underlined words sit between two groups of words, one or both of which may be a full sentence.
A word like however or although is near the punctuation.
How it works
Colon: the words before it must be a complete sentence. What follows can be a sentence, a list or a phrase that explains.
Semicolon: needs a complete sentence on both sides. A phrase without a verb, or a clause starting with although or because, cannot follow it.
However or other interrupters: if you can lift the word out and the sentence still works, put the same mark on both sides (two commas, or semicolon before and comma after).
Paired dashes or commas must match: do not open with a dash and close with a comma.
Watch out: Using a semicolon or colon because it looks sophisticated. First decide whether each side is a complete sentence; the mark follows from that.
Time: The sentence test takes seconds: cover one side of the mark and ask, can this stand alone? Do it for both sides.
Worked examples
Example 1
A complete sentence, then an explanation of it.
Which choice makes the sentence most grammatically acceptable?
ANO CHANGE
B, none of the loaves
C: none of the loavesCorrect
Dnone of the loaves
Using the technique
Before the underlined mark: “The experiment had an unexpected result” is a complete sentence.
After it, what follows explains the result: none of the loaves tasted quite the same.
A colon fits that. The original, “; although none of the loaves”, makes the second part a dependent clause (although…), which cannot follow a semicolon.