Logic For Dummies, 2nd Edition

Chapter 12

Polishing Off Your Proofs

IN THIS CHAPTER

Handling easy proofs quickly

Using conditional proof to work through moderate proofs

Giving difficult proofs a run for their money

Some logic problems almost solve themselves. Others look tough at first but soon fall in line when you know what to do. Still others resist your efforts every step of the way until you finally negotiate a solution. This chapter is all about what the Serenity Prayer calls the wisdom to know the difference. And the wisdom you gain will be the calm confidence you need to write sentential logic (SL) proofs with ease when possible and with perseverance when necessary.

Just as the American justice system declares a defendant innocent until proven guilty, I recommend the easy-until-proven-difficult approach with proofs. In this chapter, I show you how to make a quick assessment of an argument to get a gut sense of how tough it will be to prove. Next, I describe a few quick-and-dirty moves that allow you to handle the easy proofs in five minutes or less.

For more stubborn proofs, I explain how and when to pull out the conditional proof (CP) technique from Chapter 11. CP is often enough to complete proofs ...