Information in simple English

Formal fallacy

A formal fallacy is a claim that appears to be true until the rules of logic are applied. Then it dawns on oneself that it isn't the case. People are frequently misled by logical fallacies, which are used to persuade them to believe something they wouldn't otherwise.

It is also referred to as logical fallacy, deductive fallacy, or non sequitur.


Non sequitur is a blanket term for a formal fallacy that does not belong to any specific category of formal fallacies, such as affirming the consequent.

A formal fallacy may have a correct premise but an incorrect conclusion.

For illustrate, if two negatives equal a positive, why do two wrongs not equal a right?


What are the types of formal fallicices?

  • Affirming a disjunct: In this case, the conclusion does not follow the premise if first and second conditions are true. 
    • Example
      • I am either in room or I am in the home. I am in room. Therefore, I am not in the home.
      • A human is a mammal. Bat is a mammal. Therefore, Bat is a human. 2. 
  • Affirming the Consequent: In this case, if the premises and conclusion both are true. The conclusion is not necessarily dependent on the premise. 
  • Denying a conjunct: In this case, the conclusion does not follow the premise and premise does not follow up the conclusion. 
    • Example: I cannot be both in the room and in the home. I am not in the room. Therefore, I am in the home. 
  • Denying the Antecedent: In this case, if the conclusion is correct, is not compulsory for a premise that premise must be true. 
    • Example: Mr. X is a Japanese. Then Mr. X is Asian. Mr. X is not Asian. Therefore, Mr. X is not a Japanese.