JOHN LOCKE (1632-1704)

There once was a man named John Locke,

Who liked finding Cartesians to mocke.

But when those on his side

Judged that Jekyll was Hyde,

'Twas a real metaphysical shocke.

Note: In An Essay Concerning Human Understanding (1690), Locke argues that a person is “a thinking intelligent Being, that has reason and reflection, and can consider it self as it self, the same thinking thing in different times and places”.  He goes on to say that sameness of person is determined by sameness of consciousness.  He asks us to “suppose two distinct incommunicable consciousnesses acting the same Body, the one constantly by Day, the other by Night”, and claims that the Day-Man and the Night-Man would be “as distinct Persons, as Socrates and Plato”.  So Locke would say that Jekyll and Hyde are different persons.  Cartesians, who think that persons are souls, would say that Jekyll and Hyde are the same person, as long as the same soul thinks in the same body by day and by night.