I was taught that they can be used with both "very" and "much", but not with "more"
However, I saw this post and it says that using "very" with senior is incorrect. What would be the right usage of those?
There is an important distinction between "superior" and "senior" — where senior is a gradable adjective ("very senior," "very green"), superior is non-gradable, meaning you cannot assign levels to it.
See this SE thread:
Don't say: My game is much more superior to yours.
But say: My game is far superior to yours.
This is because superior is a non-gradable adjective. Non-gradable adjectives can't be used comparatively or superlatively. (In other words, you can't say or write more superior or most superior in comparison sentences.)
Colleen V. (comment):
"Much more hot" is not correct...only "much hotter". "More hot" is "hotter". "More good" is "better". We only use "more adjective" when we are forming a comparative, like "more appropriate", or "more famous". We don't use more (in standard English) with something that is already in a comparative form, like "more better", or has a single word comparative form, like "greener" instead of "more green".
Generally, you should not use any comparative language with non-gradable adjectives like superior, so both "much superior" and "very superior" are discouraged (think about how superior can be a category, like enormous or freezing — if you were describing officers in the military, you wouldn't say, "The very superior officers told the very much freezing officers to relocate the very enormous officers," since these adjectives aren't gradable).
These rules can still be broken – non-gradable adjectives can be categorized as either ‘classifying’ (ordinary; e.g. the superior officers gathered in the conference room) or ‘extreme’ (comparative; e.g. she was superior to the other officers in the room). Adverbs of maximum degree can be used with non-gradable adjectives: “she was {far, absolutely, completely, utterly, totally} superior to the other officers in the room.
The wise SE user Edwin Ashworth elucidates further:
The analysis hereabouts is very complicated. Even absolute and classifying adjectives are sometimes 'graded' because they (1) have encompassed a shift in meaning (it's very unique; he's very English) or (2) are being used quirkily (he's very dead).
The user Edinburgher in the thread you linked correctly applies the concepts Collen V. mentioned above to the word 'senior':
You can say that someone is very senior, and here "senior" is just an ordinary adjective, but if you say that someone is "senior to me", it becomes a comparative adjective.
The grass is green. ✓ ordinary adjective
The grass is greener on the other side of the fence. ✓ comparative
Now if we add emphasis with very:
The grass is very green. ✓
The grass is very much green. ✘
The grass is very greener. ✘
The grass is very much greener. ✓
The parallel here, then, is:
He is very senior. ✓
He is very much senior. ✘
He is very senior to me. ✘
He is very much senior to me. ✓
