Odd (but common) usage of “may”

[panache45]

*“I may be an adult, but sometimes I suck my thumb.”

“You may be my best friend, but sometimes I don’t like you.

“I may have a high IQ, but I can’t figure this out.”*

In all three cases, the “may” phrases describe something that’s an established fact, and the “but” phrases are the “exception to the rule.” Usually “may” phrases describe something conditional, that could be decided one way or the other, e.g. “It may rain tomorrow”. How did this alternate usage evolve?

[moriah]

Because the exceptions throw the ‘fact’ in doubt.

[Earl_Snake-Hips_Tucker]

Sounds like this is in the sense of a “concession” inusage 3. Doesn’t indicate anything about the evolution to that sense, though, and my OED is at work.

[Scarlett67]

It’s perfectly legitimate. Words often have more than one use or meaning.

@Merriam-Webster's 11th Collegiate Dictionary (bolding added)

Main Entry:may
Function:verbal auxiliary

1 a archaic : have the ability to b : have permission to you may go now : be free to a rug on which children may sprawl — C. E. Silberman — used nearly interchangeably with can c — used to indicate possibility or probability you may be right things you may need — sometimes used interchangeably with can one of those slipups that may happen from time to time — Jessica Mitford — sometimes used where might would be expected you may think from a little distance that the country was solid woods — Robert Frost
2 — used in auxiliary function to express a wish or desire especially in prayer, imprecation, or benediction long may he reign may the best man win
3 — used in auxiliary function expressing purpose or expectation I laugh that I may not weep or contingency she’ll do her duty come what may or concession he may be slow but he is thorough or choice the angler may catch them with a dip net, or he may cast a large, bare treble hook — Nelson Bryant
4 : SHALL, MUST — used in law where the sense, purpose, or policy requires this interpretation
usage see CAN