Modus Ponens and Modus Tollens Examples Fallacy

Modus Tollens Fallacy

What is Modus Tollens?

The modus tollens is a formal logical argument that occurs when one attempts to draw an inference from two premises. The second premise, which denies the antecedent, must be true for the argument’s conclusion to follow logically. It is a type of logical fallacy that occurs when one reason in the following way: If A, then B. Not-B. Therefore, not-A

The modus tollens fallacy is a formal logical fallacy which states that if the consequent of an “if” statement follows from its antecedent, then the antecedent must be true.

Modus tollens takes the form of “If A, then B. Not B. Therefore, notA.” It is an application of the general truth that if a statement is true, then so is its contrapositive. The form shows that inference from A implies B to B’s negation implies the negation of A is a valid argument.

The modus tollens fallacy is a very commonly used logical fallacy, and it is important to be able to recognize when people are committing this error.

The name of the fallacy comes from Latin, where “modus” means method or way and “tollens” means denying. Thus the meaning of the phrase roughly translates as To deny by using a certain method.

It is a type of argument that attempts to establish the truth or falsity of an assertion by assuming its contradictory and then showing that this leads to a contradiction.

Example of modus tollens fallacy sentence:

The modus tollens fallacy is a formal argument that concludes with the denial of the consequent. This fallacy takes place when someone assumes that:

Premise 1:  if A implies B

Premise 2: not-B is observed.

Conclusion: then A must be false.

Modus Tollens Examples

Modus Tollens Examples in Real Life

Example of Modus Tokens Fallacy Sentence:

Premise 1: If I have a headache, then I am sick.

Premise 1: I am not Sick

Conclusion:  I Don’t Have Headache

This is not always true because there are other reasons for having headaches.

Therefore, my conclusion does not follow.

Another example of this type of fallacy would be:

If I am in love with you, then I will give you my heart; however, it’s clear from your behavior that you don’t want me to do so

Modus Ponens

What is Modus Ponens?

Modus Ponens is a logical fallacy in which the conclusion of an argument follows from premises that are assumed to be true.  It is a form of deductive reasoning, meaning that if the premise and the conclusion are both true, then it must be valid.

Modus Ponens is a logical fallacy that occurs when an argument’s conclusion is assumed to be true because the premises are true.  It follows that;

if A, then B, and A is true, therefore B must be true.

It is a logical fallacy that occurs when one reason from an “If” statement and an “If-then” statement to the conclusion that the antecedent must be true.

This type of argument is invalid because, in order for it to be valid, both premises would have to be true, and their conjunction would have to be false, which contradicts the fact that these two statements are logically equivalent.

The modus ponens occurs in many different forms. It consists of affirming the consequent and denying the antecedent, which is two conditional statements.

The term “modus ponens” comes from Latin: it translates to “Putting the limit.” or  ‘modus’ meaning ‘way,’ ‘ponens’ meaning ‘to put,’ Thus, the name of this fallacy is mistake or error or misleading; one should not affirm anything when committing this error.

Modus Ponens is a valid form of argument, but it is also very commonly misused and misunderstood. It can be used to make an invalid syllogism.

Modus Ponens Examples

The following argument is an example of the modus ponens fallacy.

Premise1: If P, then Q
Premise 2:  P
Conclusion: Therefore, Q

It is also referred to as affirming the consequent.

Modus ponens Examples in Philosophy/Real Life

Example: The following syllogism is an example of modus ponens fallacy
Premise 1: All men are mortal
Premise 2: Socrates is a man
Conclusion: Therefore, Socrates is mortal

This argument commits the modus ponens fallacy because it assumes that all men are mortal without providing any evidence for this claim.

Another example of an argument that fits the form modus ponens:

Premise 1: If today is Monday, then Peter will go to work.

Premise 2: Today is Monday.

Conclusion: Therefore, Peter will go to work.

This argument is valid, but this has no bearing on whether any of the argument’s statements are actually true; for modus ponens to be a sound argument, the premises must be true for any true instances of the conclusion.

Modus Ponens and Modus Tollens Examples