Yes we can because if there are no ten-foot tall men, then it is indeed true that "All ten-foot tall men have brown hair"
It seems intuitively wrong that you can say "All X are Y" and yet that doesn't imply "At least one X exists".
If that is true then liar said truth.
In formal logic, but in regular English that would not be true
It seems intuitively wrong that you can say "All X are Y" and yet that doesn't imply "At least one X exists".