Comma use with contrasting expressions and tag questions

Commas are used to set off phrases that express contrast. We are showing the opposite or alternative position to the main one in the main clause.

The kittens were cute, but very messy.

Some say the world will end in ice, not fire. (from Robert Frost’s poem “Fire and Ice)

These phrases, usually beginning with but or not (and also never, seldom, or rather), show what we do not mean in contrast to what we do mean.

Using a phrase such as a contrasting expression is one way to streamline writing. Rather than repeating the whole clause structure, we can cut out repetitive words as a stylistic ellipsis. Consider the first sentence written with all the words:

The kittens were very cute, but the kittens were very messy.

Not only is it repetitive, but it can make writing monotonous, even sing, song.

When the contrasting statement comes in the middle of a sentence, it is set off by commas, before and after, because it is a strong interrupter:

The company, not the salesperson, is to blame.

Another element that adds information to a sentence, but is not part of the main clause is a tag question. Because they are not essential parts of a clause, they are set off by a comma.

Tag questions, sometimes called question tags, turn a statement into a question and are often used for encouraging a reply or for checking whether information is true or not. Tag questions ask for a yes or no response.

If the main clause is a positive statement, the tag question is negative.

If the main clause is a negative statement, the tag question is positive.

It’s cold (positive), isn’t it (negative)?

It isn’t cold (negative), is it (positive)?

If the main clause has an auxiliary verb in it, you use the same verb in the tag question.

You are coming, aren’t you?

John was there, wasn’t he?

I can come, can’t I?

You won’t be late, will you?

If there is no auxiliary verb use do / does / did (just as you do when you make a normal question).

You like coffee, don’t you?

FYI: The question tag after I am is aren’t I: I’m invited, aren’t I?

Contrasting expressions and tag questions are nonessential words or phrases, like interjections and direct address discussed in earlier posts, that are not part of our main thought or sentence. As such, they are set off by commas.

(Resources: English 3200; Margie Wakeman Wells; prowritingaid.com; perfect-english-grammar.com; englishclub.com)

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