[Lecture Two] Introduction to Logic
by Dr. Leonard Peikoff
Total Time: 2 hours, 42 minutes
Course summary: This lecture course by Dr. Leonard Peikoff provides a comprehensive introduction and overview of the study of logic. Through exercises provided to the reader and discussion of answers, the course covers definitions, syllogisms, fallacies, and the rules of generalization. It is equivalent to a university level course in logic. Read more »
In this lecture: Dr. Peikoff introduces and explains the role of fallacies in logical analysis. He provides numerous examples and concretizations of the most common fallacies as well as a discussion of wider issues relating to them.
Study Guide
This material is designed to help you digest the lecture content. You can also download below a PDF study guide for the entire course.
| What is the dual use of knowing the informal fallacies? |
| What is the difference between an appeal to authority and learning from authorities? |
| How does the argumentum ad verecundiam fallacy resemble the broader idea of subjectivism? |
| How can the appeal to “modern science” be a form of the verecundiam fallacy? |
| What is the difference between trusting an expert and fallaciously trusting an expert as a form of verecundiam? |
| Does witness testimony count as an appeal to authority or can it be relied upon? |
| What is prestige jargon and how is it used in fallacious reasoning? |
| In what way does the ad baculum fallacy attack the mind? |
| Explain how the ad hominem fallacy misdirects the process of reasoning. |
| How does psychologizing play into fallacious reasoning? |
| Explain the distinction between attacking a man’s moral character and committing an ad hominem fallacy using original examples. |
| What does the appeal to one’s own emotion consist of in practice? |
| How does the ad populum fallacy ultimately always rely on emotion? |
| What are some of the varieties of emotions used in the appeal to emotion fallacy? |
| Why is the argumentum ad ignorantium such a complicated fallacy? |
| Why are arbitrary assertions impossible to disprove? |
| What is the onus of proof principle? |
| What is the original fallacy of begging the question? What are four of its forms? |
| How does a complex question interrupt the process of reasoning? |
Q&A Guide
Below is a list of questions from the audience taken from this lecture, along with (approximate) time stamps.
| 2:10:16 | Since man’s mind is fallible, how can he be sure of the truth of any conclusion he has reached? |
| 2:10:38 | What is the distinction between a contradiction and a paradox? |
| 2:11:10 | At the end of an argument concerning the existence or non-existence of God, I invariably sum up my position by saying “just because you do not know how the world, universe, etc. originated, there is no reason to assume that it must have been started by a god.” The other person just as invariably comes back with “well, where did it come from?” At that point I’m forced to concede that I don’t know the answer. Is there a logical answer for such a mystic? |
| 2:13:03 | In her writing, Maria Montessori reveals herself to be a mystic in part. Therefore, how do you account for such a logically derived method of education? |
| 2:16:34 | What difference does it make if the facts of the universe exist independent of mind when I cannot be sure that my perceptions of the universe are correct? |
| 2:19:22 | In what sense is subjectivism an example of the stolen concept fallacy? |
| 2:21:12 | How can I be sure that I have not made an error in logic when trying to arrive at a true statement? |
| 2:22:53 | What is the difference between “metaphysical” and “ontological”? |
| 2:23:16 | You pointed out that “complex questions” are used frequently by lawyers in questioning defendants or witnesses. In that particular context, is it ever appropriate to use this or any other fallacy to question a defendant or witness? |
| 2:25:12 | What is the difference between “fact” and “opinion”? |
| 2:25:57 | Do you distinguish between “proof” and “validation” and, if so, how? |
| 2:27:07 | If you try to stir up emotion in one person to get him to believe in something, is that argumentum ad populum? |
| 2:27:33 | Re: the appeal to pity being used to excuse a criminal because he had a bad childhood: couldn’t this be determinism and not the appeal to pity? |
| 2:28:09 | Regarding your explanation of why verecundiam is wrong, if people were usually logical, would the fact that most people believe something be evidence that it’s true? |
| 2:30:45 | Is double negation a fallacy, i.e., the notion that A is not non-A. |
| 2:34:12 | Do you draw any epistemological distinction between a thoroughly proved positive and a negative that you assume to be true, since the negative cannot be proved? |
| 2:39:21 | Since a person might make an arbitrary statement that later happens to prove to be true, how can one say that a wholly arbitrary statement is false? |
| 2:40:52 | What hypothetically would constitute a proof of the existence of God? |
| 2:41:47 | Is circularity in a definition an example of begging the question? For example: “a light fixture is a fixture for producing light.” |