Consider this argument: 'The delay was caused either by the supplier or by the transporter. The despatch record shows that the supplier sent the consignment out on the agreed date. So the delay must have been caused by the transporter.' Which of the following has the same structure?

The original names two possibilities, rules one out on evidence, and settles on the remaining one. The switchboard argument does the same and is valid on the same terms. The first option slides from what usually happens to what did happen, the second argues backwards from an outcome, and the third draws a recommendation without ruling anything out at all.