Presentation 3b: Valid Argument Forms (Phil 1230A: Reasoning and Critical Thinking)

Summary

This presentation explores key valid argument forms in logic, such as modus ponens, modus tollens, hypothetical syllogism, disjunctive syllogism, and dilemmas. Each form is illustrated with clear examples, demonstrating their structures and how they function in reasoning. The presentation also highlights reductio ad absurdum as a method of argumentation and points out the common fallacy of denying the antecedent. By understanding these forms, viewers can enhance their critical thinking skills and better evaluate arguments encountered in everyday life.

Takeaways

• 😀 Valid argument forms are crucial for recognizing sound reasoning patterns.
• 🤔 Modus ponens follows the structure: If P, then Q; P; therefore, Q.
• 🌧️ An example of modus ponens: If it’s raining, you will get wet; it’s raining; therefore, you will get wet.
• 🚫 Modus tollens is structured as: If P, then Q; Not Q; therefore, not P.
• 💧 An example of modus tollens: If it’s an acid, the test strip will turn red; the test strip didn’t turn red; therefore, it’s not an acid.
• 🔗 Hypothetical syllogism structure is: If P, then Q; If Q, then R; therefore, if P, then R.
• 🍟 An example of hypothetical syllogism: If Ron eats one chip, he will eat the whole bag; if he eats the whole bag, he will be extremely thirsty; therefore, if he eats one chip, he will be extremely thirsty.
• ⚖️ Disjunctive syllogism involves: Either P or Q; Not P (or Q); therefore, the other statement is true.
• 📏 An example of disjunctive syllogism: Either Maariyah is taller than Rico, or Rico is taller than Maariyah; Rico is not taller than Maariyah; therefore, Maariyah is taller than Rico.
• 💡 Reductio ad absurdum is a method that assumes the opposite of what one wants to prove, showing it leads to a contradiction.
• 🍽️ An example of reductio ad absurdum: Assuming Flakey Chips are food leads to the absurd conclusion that wood chips should also be considered food.
• 🚫 Denying the antecedent structure is: If P, then Q; Not P; therefore, not Q, which is an invalid form.
• 📚 An example of denying the antecedent: If Bryan studies hard, then he will pass; Bryan does not study hard; therefore, he will not pass, which can be false if he cheats.

Q & A

What is the main purpose of the presentation?

The presentation aims to discuss valid argument forms and how to recognize some of the most common ones.

What is modus ponens?

Modus ponens is a valid argument form structured as 'If P, then Q. P. Therefore, Q.' It affirms the consequent based on a given condition.

Can you provide an example of modus tollens?

An example of modus tollens is: 'If it’s an acid, then the test strip will turn red. The test strip didn’t turn red. Therefore, it’s not an acid.'

What does 'modus tollens' mean in Latin?

In Latin, 'modus tollens' means 'mode that denies,' reflecting its structure of denying the consequent.

How does hypothetical syllogism work?

Hypothetical syllogism follows the structure 'If P, then Q. If Q, then R. Therefore, if P, then R.'

What is a disjunctive statement in the context of disjunctive syllogism?

A disjunctive statement asserts that either P or Q is true, and disjunctive syllogism allows for concluding the truth of one if the other is shown to be false.

What is a dilemma in argumentation?

A dilemma is an argument form that presents two options and what follows from each, concluding with a disjunction of the outcomes.

How is reductio ad absurdum structured?

Reductio ad absurdum begins by assuming that a statement is false, showing that this leads to a contradiction, and thus concludes the statement must be true.

What is the fallacy of denying the antecedent?

Denying the antecedent follows the structure 'If P, then Q. Not P. Therefore, not Q.' This is a fallacy because the premises can be true while the conclusion is false.

How can the audience engage with the content at the end of the presentation?

At the end of the presentation, the audience is encouraged to identify which form of argument is exemplified in a provided cartoon.