Is it possible to come up with a context for this sentence. "Is it a Monday today?"
I know it is usually "Is it Monday today?" but I also know that articles can be used with the days of the week. So, is that sentence possible and in what situation?
We say "a Monday" (or whatever day of the week) when we want to say that the event in question will occur on an unspecified Monday.
For example, if you said, "The next meeting of the Zetetic Society will be on Monday", that would normally be understood to mean the next, upcoming Monday. If today is Friday, that would mean three days from now. But if you said, "The next meeting will on a Monday" -- with the "a" -- that means that it will occur on Monday, but not necessarily the next Monday or any other particular Monday. Just that the day it happens will be a Monday.
Point of clarification: "The meeting will be on Monday" USUALLY means next Monday, but it could mean some other Monday if the context makes that clear. Like, "The preliminary meeting will be on June 15. Let's see, that will be a Friday. So then the full meeting will be on Monday." Presumably here "Monday" means "the Monday following Friday, June 15."
You will hear people refer to future days with an article. The common sayings are along the lines of:
In conversational settings, days of the week are generally used in the plural. Examples:
Of course as the sentences become more complex, both examples can come into play:
What's usual for me is Is today Monday? The sentence with the indefinite article is grammatical, but would differ little in practical meaning.
Consider a zoo whose entrance fee is free on Mondays. You call and order tickets and are informed of the free day. You could say 'Is today (or tomorrow, etc) a Monday?' Or something like 'Is that day a Monday, by any chance?'
One sentence that sounds idiomatic is the ellided response on a Monday
What day does Christmas fall on this year?
(Christmas falls on a Monday this year.)