Critical Thinking Course...Philosophy In Chapter 8, we learned the basics of truth-functional logic. It is important to remember that the purpose of truth-functional logic is to determine which arguments are valid and which are invalid, and common invalid forms are known as truth-functional fallacies. Consider the following question. Which of the following is a well-known truth-functional fallacy? (Points : 4) a. Modus tollens b. Modus ponens c. Valid chain d. Denying the consequent Solution.