Formal versus Informal Fallacies

Click Chapter4.pdf link to view the file.

Read section 4.1 (p. 185-186) to learn the difference between formal and informal fallacies and learn two key formal fallacies that look like good logic, but are not: denying the antecedent, and affirming the consequent. 

There is a popular joke among philosophers about Descartes (the French philosopher who famously wrote "I think, therefore I am") walking into a bar and, when the bartender asks if he’d like a drink, replying "I think not" and vanishing in a puff. While delightful to share among your philosopher friends, this joke actually falls prey to one of these fallacies – see if you can tell why.