How did 'unless' evolve to mean 'if not'?
[Etymonline:] mid-15c., earlier onlesse, from on lesse (than) "
on a less condition (than); see less. The first syllable originally on, but the negative connotation and the lack of stress changed it to un-. ...
[†A.] 2. Forming a conjunctional phrase introducing a case in which an exception to a preceding (or following) statement will or may exist: except if, if..not.
1. How did
on a less condition (than) shift to mean if not?
2. What and where is the 'negative connotation'?