Yesterday morning and last night

I received the following text from my son who is presently teaching English in Japan:

A student wrote, “I cleaned my room last morning” and my JTE corrected it to “yesterday morning.” So then the student asked, why “last night” is OK, but “last morning” isn’t. Do you have an explanation? Why do evening and night get attached to “last,” but morning and afternoon get attached to “yesterday?”

This is not the first time he has had a question about erratic and inconsistent English grammar. This is one of the beauties and frustrations about teaching English in a foreign country. This morning JB and I puzzled over this while eating breakfast.

JB thought it had something to do with night being part of two days, the previous one and  the present one, so it made more sense to say “last night” because “yesterday night” would make no sense. Which part of the bifurcated night would it refer to? Also I thought saying “…day night” would be strange, unclear, and contradictory, whereas “yesterday morning” and “yesterday afternoon” actually referred to the previous day. I actually think saying “yesterday evening” is correct, which would make this explanation valid.

Now all of this is rather humorous, especially in this 21st century when I am talking or texting in actual time with my son who is halfway across the world actually 14 hours in the future. So his yesterday morning is my tonight.

I’m not sure we have an answer regarding this grammatical question, but there is something intriguing about why we say the things we do. These kinds of confusions clearly make communication complicated but provocatively layered. And it is in these layers where the poetry lies (or is it lays?).

At least that’s what we were thinking “this,” but IB’s “yesterday,” morning.