Formal fallacies

Question 1

What is a fallacy?

Answer 1

This is an argument that is imperfect in some way.

Question 2

What is the difference between a formal fallacy and an informal fallacy?

Answer 2

A formal fallacy arises from faulty reasoning - it is about the structure of the argument. An informal fallacy are not concerned with anything strictly logical.

Question 3

What are the three types of formal fallacies?

Answer 3

1. affirming the consequent
2. denying the antecedent
3. fallacy of composition

Question 4

What is a modus ponens structure?

Answer 4

If P then Q
P
Therefore Q

Question 5

What is a modus tollens structure?

Answer 5

If P then Q
Not Q
Therefore not P

Question 6

Are modus ponens and modus tollens valid?

Answer 6

Yes

Question 7

Explain what ‘affirming the consequent’ fallacy is and give an example

Answer 7

This is when we attempt to use the modus ponens but instead of asserting the antecendent of the conditional, we assert the consequent:
If P then Q
Q
Therefore P

This is not valid

Question 8

“If P then Q”

What is the consequent and what is the antecedent?

Answer 8

The consequent is the second statement and the antecedent is the first statement

Question 9

Explain what ‘denying the antecedent’ fallacy is and give an example

Answer 9

For a modus tollens argument, we need to deny the consequent, not the antecedent. Denying the antecedent does not show that the consequent is false:
If P then Q
Not P
Therefore, not Q

This is not valid