Now that/because/as you mention it: 'that' meaning 'because'

Question

Now that you mention it.

Now because you mention it.

Now as you mention it.

I've seen many times that being used in place of because and as, mostly by the native speakers.

Answer 1

I would say "now that" is actually being used instead of "because", not "now because".

Another appropriate start to this sentence is "since".

If you've seen "now" and "because" starting a sentence, perhaps it was "now, because you've mentioned it," which would be acceptable. Note that it's colloquial and places extra emphasis on the fact that they wouldnt be telling you whatever they are about to say if you hadn't mentioned "it"

"Now as you mention it" is not something I would say. However, you might say, "As you mentioned..." but it has a slightly different meaning. The other examples are leading up to something related to what was mentioned, where as "as you mentioned" instead would be followed by the same thing already mentioned.

Answer 2

Personally to me, the version with because sounds extremely weird and the one with as quite weird, without some follow up. Let's take a look at some corpora.

CoCa seems to agree with me, having no occurrences of either the version with because or as. Actually the query "Now * you mention it" only finds "that" (roughly a 100 matches) and looking for "Now you mention it" finds 5 matches.

The Hansard corpus has only 1 match for "Now that you mention it" and none for the because or as, but given that it's British Parliamentary speeches this makes some sense (you can get a couple more hits if you also choose a wildcard for "you").

Answer 3

IMHO differences between those are as if difference between yes and of course. It depends on a situation. When you talk to some close person for you, I mean informal language, you can say that. But if your dialog is formal, you should say as or because. There are no big differences.