That the logical relation, as it is expressed by the proposition ' Socrates is tanned ', is truly a relation of identity is a result of the designation of the terms in the proposition :
While the full extension of the term (that is, when the term is taken as not being used in a proposition, or in any other context) ' tanned ' is all individual tanned beings, the term ' Socrates ' restricts the actual scope of the term ' tanned ', it restricts it to the individual Socrates only. So both the subject term ('Socrates') and the predicate term ('tanned') designate the same (namely the individual, called 'Socrates'), and consequently these terms can be identified with each other. And that is, they can be logically identified with each other.