You don’t have to cite anyone when you write ‘on the one hand’ or ‘on the other.’ And as my son once observed (please note the citation), no one knows who was the first person to say ‘see you later, alligator.’ But perhaps I should take that back. Maybe somebody does know. Maybe I am just the one who does not know. It sounds like it might have come from one of those Tin Pan Alley songs in the twenties.
Douglas Wilson