The correctness of the formal logic comes from the way we built the rules from valid arguments. Proving it's complete is far more difficult. Methods to make it easier Our logic is complete, but still not very practical to use. Here are some tricks to make it easier. Here it's easier to first rewrite the argument into an equivalent argument.
R are equivalent.
This trick is called the deduction method . Additional deduction rules As we have seen, any valid argument could be transformed into a new rule. Here are two useful rules. P ' Adding those new rules won't change the power of the formal logic, but can make it more convenient. On the other hand, a minimal formal logic is nice since it's less error prone, and it's easier to remember all the rules.