"so" and "this" as adverbs meaning "to a degree"

Question

Recently, a non-native speaker asked me whether they should say "Why is it so cold?" or "Why is is this cold?". While clearly the former is much more common, I struggled to explain why. Cambridge Dictionary gives:

This: as much as shown or to a particular degree

So: very, extremely, or to such a degree

which doesn't help much to clear things up. The problem is that in the person's native language, both are expressed using the same word. Come to think of it, most languages I know of do not seem to distinguish between them.

How should I explain the difference in usage?

Answer 1

The source you have cited should be good enough to differentiate.

"Why is it so cold?"

Firstly, it is very cold. "Why is it so?"

"Why is it this cold?"

(It may not be very cold, it need not be). Just "Why is it as cold as it is now?"

Compare:

Do you always have your coffee so hot? (It's very hot.)
Do you always have your coffee this hot? (As hot as it is now.)