This is part 4. You should see part 1, part 2, and part 3 before reading this. This is also written with the assumption that you already know propositional logic.

Natural deduction is the use of rules of inference and assumptions in order to reach a conclusion, and they are used to prove argument forms to be logically valid. The entire reasoning process is made entirely explicit, and is known as a ‘proof’ or ‘derivation.’ I will assume here that you already know how to use natural deduction in propositional logic, and natural deduction in predicate logic is done in the same way as in propositional logic, except some additional rules of inference are needed. (more…)