ABSTRACT
There are various kinds of logical inference that cannot be justified on the basis of the propositional calculus; for example:
1. Any friend of Martin is a friend of John.
Peter is not John’s friend.
Hence, Peter is not Martin’s friend.
There are various kinds of logical inference that cannot be justified on the basis of the propositional calculus; for example:
1. Any friend of Martin is a friend of John.
Peter is not John’s friend.
Hence, Peter is not Martin’s friend.