In that instant VS In that moment

Mr. TomIn that instant, just for a moment, if I knew she was lying.

Mr. TomIn that moment, just for an instant, if I knew she was lying.

Mr. TomWould you say both of these are the same? And natural?

Yes, I would. The only problem is that they're not sentences.

These don't sound right. The basic problem is the juxtaposing of the phrases "in that instant" and "just for a moment." These phrases cannot logically be put together like this in English. Furthermore, the phrase "in that moment" is usually not used in English in a situation such as this. You would instead say something like the following:

In that instant, I knew she was lying.

In that instant, just for a moment, if I knew she was lying.

Thanks, Avangi and Anon.

Sorry, I think I missed out the word "only" in both sentences. How do these sentences sound to native ears now?

In that instant, just for a moment, if only I knew how it felt like to be a mother.

. . . . if only I knew how it felt to be a mother. These are still really not sentences. There's no main clause.
. . . . if only I knew what it felt like to be a mother, [perhaps I'd be more sympathetic to her problems.] .

(I suppose they could be exclamatory sentences.) Ah! If only you knew! (conversational)

The new sentences are not grammatical, or even logical. You cannot juxtapose the phrases, "in that instant" and "just for a moment/an instant," like this. And the phrase "in that moment" is not used like this. Also the words "just" and "only" - in that order - are not used in the same sentence.

Mr. TomWould you say both of these are the same? And natural?
In that instant, just for a moment, if I knew she was lying.
In At that moment, just for an instant, if I knew she was lying.

I would say that they are both the same (as modified above). Yes.

The logic of comb

AnonymousYou cannot juxtapose the phrases, "in that instant" and "just for a moment/an instant," like this.

A lot of accomplished novelists will be saddened to hear this news.