Proof Strategies and Rules of Thumb

Copi, Cohen, & Rodych's Rules of Thumb

• B.T.I.W

1. Begin deducing conclusions from the given premises by the given rules of inference.

2. Try to eliminate statements that occur in the premises but not in the conclusion.

3. Introduce by means of Addition a statement that occurs in the conclusion but not in any premise.

4. Work backward from the conclusion by looking for some statement or statements from which it can be deduced. Then try to deduce those intermediate statements from the premises

Rodych's Rules of Thumb for Executing Proofs

1. Look first at the conclusion.

2. If the conclusion is a simple statement.

3. If the conclusion is a compound statement.

4. Work backward from the conclusion.

5. Determine the main logical operators of each premise.

6. Don't get overwhelmed by complex compound statements.

7. Know your Rules of Replacement

8. Conjunctions are vert useful

9. Look for the same collections of simple statements!

10. Know how to use distribution!

Woods, Irving & Walton's Proof Strategies

1. Identify argument forms that correspond to valid tules of inference.

2. Break long proofs into a series of shorter subproofs.

3. Try to use simple statements early and often.

4. Look for propositions that are repeated

5. Work both from the top down and from the bottom up, epsecially in long proofs

6. Recall that some rules introduce connectives while others eliminate them

7. You cannot use C.P or I.P until the very end of Logic 1000. When stuck, or when a result needs to be proved in the absence of premisesm use Conditional Proof (C.P) or Indirect Proof (I.P)

TBA