Well, existential types are pretty similar. If you've got (exists a . a) then you have to be prepared for it to be a float, but also prepared for it to be a lis

Well, existential types are pretty similar. If you've got (exists a . a) then you have to be prepared for it to be a float, but also prepared for it to be a list, or a string, but also a tuple, some type for which we only know that it is a monad, and everything else :) More specifically, we've lost any information to tell us what specific thing might be here so we have to be prepared for any answer. It's the inverse of (forall a . a) which we can ask to become whatever we like.