Can I use "...that is" in a professional writing piece?

Imho, ‘that is’ is not needed. It slows down the reader and keeps you from getting to the really good part of the sentence- the part where something happens.

I would drop the ellipses and and the “that is” and just the run the sentence through with no semi-colon.

@janbb I agree, but should I make a comma in that case? Like this:

“it seemed as if nothing could go wrong, until _____” or without the comma before until?

For some reason I’m having a lot of trouble with this.

No, you don’t have two separate ideas so you don’t need a comma.

You do need the comma. Otherwise the reader doesn’t know to pause.

Is this fiction or fact, a short story or essay, journalism or diary? The sentence as written is a cliché, with out without the comma.

True that.

@gailcalled @acidlogik It is a narrative essay. What better way is there to suggest such a point?

@HeroicZach”: Tell us precisely what went wrong; then we can work backwards.

(Is a narrative essay fiction?)

Why don’t you give us the whole sentence and then we have a better idea of how to help?

I.e.

@gailcalled It is a factual narrative.
@janbb As you wish:

It seemed as if nothing could go wrong…that is, until the doctor came in and gave the bad news.

You can use “that is.” But lose the ellipses if you can. An em dash would serve you just as well there and without any ambiguity. In a professional piece, you might want to reserve ellipses for use in their formal function as indication of an omission or, if absolutely necessary, as a thought that trails off. The type of piece and the intended publication should determine whether you want to take that liberty.

I agree that a little more context would help. If you are a pro, I imagine you can find a workaround for this entire construction. One of my watchwords as an editor is “When in doubt, dodge it.”

@Jeruba Great advice on writing as usual.

With professional writing, avoid using the word ‘that’.
In the example you could use the word, ‘until’. Just leave out the ‘that is’.

??? @basp, can you explain why you’d say to avoid “that”? That is such an extraordinary piece of advice that I can’t say I have ever heard it before in my life. As a principle, I don’t think it is one that would be that easy to comply with; that is, I think that it would be impossible to sustain any piece of writing for very long without some use of that word.

@Jeruba And that’s all you have to say about it! :-)

Jerba
There are times when the word ‘that’ is appropriate, however, in professional writing those instances are few and far between. Generally, the sentence is less clumsy and reads smoother without it.
I can’t cite a particular “rule”, it’s just the way I was taught in college.

@basp: (It’s Jeruba). Ain’t that the truth?

I have to say that the way someone was taught in college does not present a stronger argument to me than the best writing I read in top magazines, journals of fiction, and distinguished novels.

An arbitrary guideline to avoid some particular word is not helpful; rather, the important thing is to know why you are using the words you use and make the best word choices for the particular situation.