A phrase as an interjection

Question

Often in spoken English, I see one sentence or phrase "set up" another much like an interjection. For example:

I forgot to ask. Did you find that book I told you about?

How do you generally punctuate this? I've seen a comma used for this, but I that's only correct if it can be argued that I forgot to ask is a proper interjection (can it be?).

Should I use a colon? Semi-colon? Does it matter?

Answer 1

You could punctuate this in a few ways, in decreasing levels of formality

With a colon (:)

I forgot to ask: did you find that book I told you about?

With a dash (–)

I forgot to ask—did you find that book I told you about?

With an ellipsis (…)

I forgot to ask…did you find that book I told you about?

The colon is the most formal, the ellipsis quite informal. I personally would use a dash. The ellipsis here is used to indicate a pause or an unfinished thought, which some purists might object to (claiming that an ellipsis can only be used to indicate something which has been left out).

Answer 2

You can certainly use a colon.

I forgot to ask: did you find that book I told you about?

Technically, using a semi-colon would not be grammatically incorrect (both parts being complete sentences), but it wouldn't really fit the situation.

Answer 3

I would use a comma:

I forgot to ask, 'Did you find that book I told you about?' (comma, direct speech)

One could rewrite it using indirect speech as well:

I forgot to ask whether you found that book I told you about (indirect speech)