Affirming the consequent

Affirming the consequent, sometimes also called asserting the consequent or the converse error, is a type of logical fallacy where a premise is asserted as true simply because a conclusion implied by the premise is true. This is a fallacy because it assumes that the conclusion could only have been reached in one particular way.

For example:
 * If an animal is a rat, then it has four legs
 * My dog Lassie has four legs
 * Therefore, Lassie is a rat

Formal Construction

 * A implies B
 * B
 * Therefore, A

Further Examples

 * Creationism example 1
 * If the universe was created by God, then there would be order and natural laws observed in the universe
 * We see examples of order and natural laws in the universe
 * Therefore, the universe was created by God

This argument assumes that a deity is the one and only explanation for order in the universe. And even if we do assume that a deity is the only explanation, it doesn't automatically mean that it must be the Christian deity. The Flying Spaghetti Monster is a good counter-example that satirically exposes the underlying fallacy of this argument.


 * Creationism example 2
 * If the Biblical flood story is true, then there was a boat built with the dimensions described in the Bible
 * We found a boat with these dimensions
 * Therefore, the Biblical flood story is true.

To see why this is a fallacy, consider the same logic applied to the story of Cinderella and the existence of Cinderella's castle in Disneyland.