[Lecture Four] 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: This lecture begins the discussion of deductive reasoning and the formal analysis of logical reasoning. Dr. Peikoff explains the difference between the validity and truth of an argument and why it matters to logic. He reviews the standard forms of deductive reasoning.
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 distinction between inductive and deductive reasoning? |
| What is the difference between the validity of an argument and the truth of an argument? |
| Why is truth only applied to the premises or conclusion specifically? |
| What are the two conditions for determining the truth of a conclusion? |
| What are the three classifications of statements that make up the main types of deductive arguments? |
| When determining the validity of the argument, what is the most important element to isolate? |
| Using original examples, explain the four possibilities of arguments in the mixed hypothetical type, indicating why two are valid and two are not. |
| How can one become attuned to the process of translating ordinary language statements into standard form logical arguments? |
| When analyzing an argument, why is it important to find the conclusion first? |
| In the weak alternative argument, how can one be sure that the form is valid? |
| How can one identify when an argument is a weak or a strong alternative? What if you cannot tell? |
Q&A Guide
Below is a list of questions from the audience taken from this lecture, along with (approximate) time stamps.
| 1:45:25 | Concerns regarding whether exercise #5 committed verecundiam. |
| 1:46:52 | Please restate the difference between composition and generalization. |
| 1:48:06 | Is it the fallacy of composition to say that the universe possesses identity on the basis of the following argument? “Everything that exists possesses identity, therefore the universe itself possesses identity.” Is that an example of a fallacy? |
| 1:49:55 | Do you regard the advertising of basically undifferentiated products as necessarily illogical when they attempt to establish associations to other products? |
| 1:52:12 | Is there a difference between “the impossible” and “the not possible”? |
| 1:55:57 | Is JFK’s “ask not what your country can do for you, but what you do for your country” statement an example of a false alternative? |
| 1:56:24 | Many comedians rely on the use of informal fallacies for their humor. Is that okay? |
| 1:57:05 | Would a non-Objectivist logician define the fallacy of ignorantiam the same way you did? |
| 1:58:40 | What led a logician like Aristotle to opt for the unmoved mover as opposed to eternal existence? |