I regularly say "this is the stairs". "Stairs" can act as a collective singular noun in situations like this in some varieties of English, but the answer is not accepted.
Correct me if I'm wrong,not a native speaker of english here, but i think if we want to use it in singular as a collective noun we use a flight of stairs,staircase,stairway.Not very sure if we can say, for instance, "where does this stairs go?" instead of "where do these stairs go?"
As a native English speaker, I agree with StellaNtal. But I also did a google search and "this is the stairs" doesn't register on the Ngram scale and google search just switches it over to "these..." So, it's not used broadly enough to be included.
No, the difference occurs here because the English word "stairs" is plural but the Greek word "σκάλα" is singular.
So plural would be οι σκάλες when would that be used. Just for 2 or more staircases?
That's right and then we would only use..."staircases" as in "That building has three staircases."
The English word stairs is plural, but it can also be used in the singular without the plural s. So "this is the stair" should be counted as correct.
See Merriam Websters dictionary: "Definition of stair 1 : a series of steps or flights of steps for passing from one level to another —often used in plural but singular or plural in construction"