Why is "today morning" wrong but "tomorrow morning" right?

I have heard "today morning" being said in the country I am from a lot. However here in the States people never use it and correct others who do. "Tomorrow morning" is acceptable though.

What is the correct usage and why?

Solution 1:

Both are correct, in that "today" and "tomorrow" are both adjectives which describe "morning". However, it's not commonly said in the States, so it sounds odd to native speakers, who would usually say "this morning".

So the answer to your question is that "today morning" is grammatically correct but not the preferred idiom in American and British English.

Solution 2:

For times of day closest to now, it's natural in most dialects of English to use words such as this next to the word. Thus you get 'this morning', 'last night', etc.

For other times, the actual word denoting that day is used next to the time of day - tomorrow morning, Saturday evening, etc.

While it might be logical to say today morning, Western English-speakers are only used to the shortened or what they'll say, idiomatic, usage: this morning.

Further, one general pattern in English is to use the shortest way of expressing something. Simple as!

Hope this helps.