https://en.wikipedia.org/wiki/Generic_property Nice examples of “duals” here which I think of as: ” But on the other hand…” “There are many different notions of “generic” (what is meant by “almost all”) in mathematics, with corresponding dual notions of “almost none” (negligible set); the two main classes are: In measure theory, a generic property is one that holds almost everywhere, with the dual concept being null set, meaning “with probability 0″. In topology and algebraic geometry, a generic property is one that holds on a dense open set, or more generally on a residual set, with the dual concept being a nowhere dense set, or more generally a meagre set.”

“There are many different notions of “generic” (what is meant by “almost all”) in mathematics, with corresponding dual notions of “almost none” (negligible set); the two main classes are:

In measure theory, a generic property is one that holds almost everywhere, with the dual concept being null set, meaning “with probability 0”.

In topology and algebraic geometry, a generic property is one that holds on a dense open set, or more generally on a residual set, with the dual concept being a nowhere dense set, or more generally a meagre set.”