Why Is Affirming the Consequent Invalid?

Modus ponens

is a valid argument form

argument form

A logical argument, seen as an ordered set of sentences, has a logical form that derives from the form of its constituent sentences; the logical form of an argument is sometimes called argument form. ... In argumentation theory or informal logic, an argument form is sometimes seen as a broader notion than the logical form.

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Logical form - Wikipedia

in Western philosophy because the truth of the premises guarantees the truth of the conclusion; however, affirming the consequent is an invalid argument form because the truth of the premises does not guarantee the truth of the conclusion.

What is affirming the consequent examples?

Affirming the consequent, sometimes called converse error, fallacy of the converse, or confusion of necessity and sufficiency, is a formal fallacy of taking a true conditional statement (e.g., "If the lamp were broken, then the room would be dark,") and invalidly inferring its converse ("The room is dark, so the lamp ...

What is denying the antecedent and affirming the consequent?

Like affirming the consequent, denying the antecedent is also a fallacious form of reasoning in formal logic. ... Denying the antecedent makes the mistake of assuming that if the antecedent is denied, then the consequent must also be denied.