Affirming the Consequent
What is Affirming the Consequent?
You open the curtains in the morning and see that the pavement outside is soaking wet. “It must have rained last night,” someone says. Rain can certainly make the pavement wet, but the reverse does not follow. A street-cleaning truck may have just passed, a neighbour may have hosed down the balcony, or an underground water main may have burst. The pavement would be wet either way. Assuming that the first event must have happened because its usual result has occurred is the reasoning error known as affirming the consequent.
Affirming the Consequent: common mistakes and how to handle them
A HR manager points to the company policy and says, “If someone uses the expedited process, the application will be approved that same day. This one was approved today, so they must have used the expedited process.” But the system sometimes clears its queue, allowing a standard application to be processed within the day. A parent checks the front-door access log and says, “If the kids get home on time, the security system sends an alert. An alert just came through, so they must have come through the door.” In fact, a grandparent used the same access card while heading out for a walk. Both mistakes come from assuming that a result can be produced in only one way.
What the Affirming the Consequent questions test
Whether the stated condition supports reasoning in the reverse direction; whether the argument wrongly infers a single cause from an observed result; and whether the result described in the question could have been produced by other means. The examples often involve company procedures, system alerts, and everyday assumptions about how things happen.