Grammar

Concrete nouns are nouns that refer to people, animals, or things. Concrete nouns can be "re-identified" with the idea of "the very same one".

That is the same [person / animal / thing] that I saw yesterday.

morning does not fit the profile for such a noun. It's not a person, animal, or thing. You can't say that the morning of December 25, for example, is the s

I've found several opinions which discuss countable/uncountable in connection with concrete/abstract, claiming that certain nouns are ambivalent (Should I not mix chemistry and grammar?). In "The last three mornings have been foggy," I'm inclined to take "mornings" as concrete.

I was unable to find "morning" addressed specifically, but Google includes one of MrM's posts in which he foun

But a concrete noun can be uncountable (luggage) while an abstract noun can be countable - being one doesn't correspond to being another.

Grammar Geek being one doesn't correspond to being another.

Absolutely so. It's not that simple. I came across a number of references in which both concepts were discussed, and one was employed by way of describing certain aspects of the other. Perhaps I can find them again, if I haven't scuttled my history.

I think it would be at least limited

CalifJim You can't say that the morning of December 25, for example, is the same morning you are experiencing again today. So morning is an abstract noun.

Nor can I say that the egg I ate yesterday is the same egg I'm eating today. (Oh dear.)

- A.

AvangiNor can I say that the egg I ate yesterday is the same egg I'm eating today. (Oh dear.)

Be reasonable! You can say that the egg you didn't eat is that very same egg that you colored for Easter. At least somere-identification of eggs upon re-experiencing them is possible! Now individual peas, I don't know.

What is "morning"? Is two o'clock in the morning the same sort of "morning" that 11:30 in the morning is? Can you visually identify "morning" as being a "morning" with 100% certainty? And what about when we change the clocks? What might have been morning yesterday might be afternoon today (or vice versa).
To me, "morning" is much too abstract to be concrete.