Mr. Nance,
My question has to do with Lesson 24. Exercise 22 has the students do a challenge, testing the validity of all 256 forms. I understand it’s to practice counterexample. Is there another reason not to put this challenge after lesson 26 after they’ve learned all the rules? (Which I think would make it easier.) Continue reading Counterexample challenge
Introductory Logic Lesson 23 introduces the concepts of validity and soundness. The lesson says that a syllogism is valid if and only if the premises imply the conclusion. If a syllogism can have true premises and a false conclusion, the argument is invalid. A sound argument is a valid argument with all true statements.
The only purpose of Lesson 23 is to introduce the concepts of validity and soundness. This lesson does not explain how to determine validity. So if after studying this lesson you have trouble knowing whether a given syllogism is valid or invalid, don’t worry about it. You will learn how to do that in the next three lessons. Lessons 24-26 are dedicated to teaching the methods for determining the validity of a syllogism.
Teaching students how to translate syllogisms into standard categorical form occupies several lessons in Introductory Logic. Lessons 11 and 12 explain how to translate categorical statements into standard form, which is then emphasized while learning about the Square of Opposition in Lessons 13-18. Lesson 19 teaches students how to distinguish premises and conclusions, in part so that in Lesson 20 they will understand how to identify the major and minor premises, so that they may know how to arrange a syllogism in standard order. Finally, Lessons 21 and 22 teach them how to identify the syllogism form using mood and figure. All this occurs before the students begin to learn how to determine the validity of a syllogism. Continue reading Why Standard Form?
The Square of Opposition is a useful tool for representing and understanding the relationships between categorical statements with the same subject and predicate:
The relationships are defined this way:
Contrariety: The statements cannot both be true, but can both be false.
Contradiction: The statements cannot both be true, and cannot both be false.
Subcontrariety: The statements can both be true, but cannot both be false.
Subimplication: If the universal is true, the particular must be true.
Superimplication: If the particular is false, the universal must be false.
Students might be interested to discover that the square of opposition can be created for non-categorical statements as well. Continue reading The Square of Opposition (for logic nerds only!)
Hello, Mr Nance!
Could you please explain to me why the tests and quizzes pack for the Introductory Logic has a test form A and a test form B for the same chapters? I am sure it is logical (pun intended) but I am not getting it and just want to be sure I am administering them correctly.
Thanks in advance! Continue reading Why Logic Test A and B?
Mr. Nance,
I have a question on Intermediate Logic, Test 2, Form B, Problem 4. The question says: “An invalid argument can have true premises and a true conclusion, is this true or false?” The answer book says it’s true but the definition of an invalid argument would prove that statement to be false. Is there a typo or is that correct? Continue reading Invalidity and truth
Lesson 10 of Introductory Logic discusses the possibility that two statements delivered by different people may seem to be inconsistent, but upon further examination turn out to actually be consistent. We can call these seeming disagreements, and they can happen in one of two ways. Continue reading A Seeming Disagreement
I teach logic online. In addition to my regular logic students I have several Classical Conversations tutors who audit my logic course. After I finish the lesson and my students leave, the auditors join the class live, turning on camera and mic, and we discuss the lesson. I appreciate these discussions, because I often learn as much from them as they do from me. Continue reading I Know London is the Capital of France
A good introductory logic course will discuss the importance of defining terms in any argument. One clear demonstration of using definition in argument is Martin Luther King Jr.’s “Letter from Birmingham Jail,” a letter which King directed at Christian pastors in Alabama in 1963 defending his campaign of nonviolent direct action. Continue reading Defining Terms from Birmingham Jail
Mr. Nance,
Regarding question no. 10 on page 252: What is the reason for its invalidity? Does the pure hypothetical syllogism also use the five rules of validity? The argument is:
If he is the Antichrist, then he opposes God’s people.
If he is the Beast, then he opposes Gods people.
Therefore, if he is the Antichrist, then he is the Beast.
Is the Beast major term? And is the Antichrist the minor term? How do we make it into valid categorical syllogism? Continue reading The Antichrist and the Beast Syllogism