Why is denying the antecedent invalid?

Asked By: Jackqueline Kallichuran | Last Updated: 29th February, 2020
Category: technology and computing information and network security
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Like modus ponens, modus tollens is a valid argument form because the truth of the premises guarantees the truth of the conclusion; however, like affirming the consequent, denying the antecedent is an invalid argument form because the truth of the premises does not guarantee the truth of the conclusion.

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Keeping this in view, is denying the consequent valid or invalid?

Affirming the Consequent” is the name of an invalid conditional argument form. You can think of it as the invalid version of modus ponens. No matter what claims you substitute for A and B, any argument that has the form of I will be valid, and any argument that AFFIRMS THE CONSEQUENT will be INVALID.

Similarly, what is antecedent argument? Description: It is a fallacy in formal logic where in a standard if/then premise, the antecedent (what comes after the “if”) is made not true, then it is concluded that the consequent (what comes after the “then”) is not true. Logical Form: If P, then Q.

Similarly, is denying the disjunct valid?

For a brief introduction to propositional logic, see the entry for Propositional Fallacy. However, affirming a disjunct in order to deny the other is non-validating: if both disjuncts are true, then the premisses of the argument will be true and the conclusion false?but see "Types of Disjunction", below.

What is the difference between affirming the consequent and denying the antecedent?

John will want to marry Mary is the consequent. Denying the antecedent means denying John loves Mary. In other words John does not love Mary. Affirming the consequent means asserting John will want to marry Mary.

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What is a straw man argument example?

Straw Man Fallacy Examples. The basic structure of the argument consists of Person A making a claim, Person B creating a distorted version of the claim (the "straw man"), and then Person B attacking this distorted version in order to refute Person A's original assertion.

What makes an argument valid?

Validity and Soundness. A deductive argument is said to be valid if and only if it takes a form that makes it impossible for the premises to be true and the conclusion nevertheless to be false. In effect, an argument is valid if the truth of the premises logically guarantees the truth of the conclusion.

What is inconsistency fallacy?

The inconsistency fallacy is an argument that includes a contradiction, which is to say that it has various propositions that cannot be true at the same time. Logically Fallacious.

What is antecedent critical thinking?

Chain or Hypothetical Argument
An argument composed entirely of conditional claims (premises and conclusion). When valid, the premises are arranged so that the consequent of one premise becomes the antecedent of the next.

Can a valid argument have a false conclusion?


FALSE: A valid argument must have a true conclusion only if all of the premises are true. So it is possible for a valid argument to have a false conclusion as long as at least one premise is false. 2. A sound argument must have a true conclusion.

What is discrete math fallacy?

Fallacy. A fallacy is an incorrect result arrived at by apparently correct, though actually specious reasoning. The great Greek geometer Euclid wrote an entire book on geometric fallacies which, unfortunately, has not survived (Gardner 1984, p. Barbeau, E. J. Mathematical Fallacies, Flaws, and Flimflam.

What is begging the question fallacy?

The fallacy of begging the question occurs when an argument's premises assume the truth of the conclusion, instead of supporting it. In other words, you assume without proof the stand/position, or a significant part of the stand, that is in question. Begging the question is also called arguing in a circle. Examples: 1.

What is an example of a formal fallacy?

Most formal fallacies are errors of logic: the conclusion doesn't really “follow from” (is not supported by) the premises. Either the premises are untrue or the argument is invalid. Below is an example of an invalid deductive argument. Premise: All raccoons are omnivores. Conclusion: All raccoons are black bears.

What is a disjunctive syllogism examples?

A disjunctive syllogism is a valid argument form in propositional calculus, where and are propositions: For example, if someone is going to study law or medicine, and does not study law, they will therefore study medicine.

What does false dichotomy mean?


A false dichotomy is a dichotomy that is not jointly exhaustive (there are other alternatives), or that is not mutually exclusive (the alternatives overlap), or that is possibly neither. Note that the example given above is not mutually exclusive, since the test and the program could both be wrong.

What is hypothetical syllogism critical thinking?

In classical logic, hypothetical syllogism is a valid argument form which is a syllogism having a conditional statement for one or both of its premises. An example in English: If I do not wake up, then I cannot go to work.

What is a disjunct in an argument?

Disjunct: One of the propositional components of a disjunction. Description: Making the false assumption that when presented with an either/or possibility, that if one of the options is true that the other one must be false. This is when the “or” is not explicitly defined as being exclusive.

What is a false dilemma fallacy?

False Dilemma is a type of logical fallacy, which is a belief or claim based on mistaken reasoning. False Dilemma is a fallacy based on an "either-or" type of argument. Two choices are presented, when more might exist, and the claim is made that one is false and one is true-or one is acceptable and the other is not.

What is the logical form of affirming the antecedent?

In committing the fallacy of affirming the consequent, one makes a conditional statement, affirms the consequent, and concludes that the antecedent is true. Affirming the antecedent of a conditional and concluding its consequent is a validating form of argument, usually called "modus ponens" in propositional logic.

What makes an argument inductive?


An inductive argument is an argument that is intended by the arguer to be strong enough that, if the premises were to be true, then it would be unlikely that the conclusion is false. So, an inductive argument's success or strength is a matter of degree, unlike with deductive arguments.

What is the difference between a valid argument and a sound argument?

What is the difference between a sound argument and a valid argument? An argument form is valid if and only if whenever the premises are all true, then conclusion is true. For a sound argument, An argument is sound if and only if it is valid and all its premises are true.

What is antecedent and consequent?

A consequent is the second half of a hypothetical proposition. In the standard form of such a proposition, it is the part that follows "then". In an implication, if P implies Q, then P is called the antecedent and Q is called the consequent.