 Proponents of this point of view point out that even deductive inference cannot be justified deductively. Consider Lewis Carroll’s dialogue between Achilles and the Tortoise (Carroll 1895). Achilles is arguing with a Tortoise who refuses to perform modus ponens. The Tortoise accepts the premise that p, and the premise that p implies q but he will not accept q. How can Achilles convince him? He manages to persuade him to accept another premise, namely “if p and p implies q, then q”. But the Tortoise is still not prepared to infer to q. Achilles goes on adding more premises of the same kind, but to no avail. It appears then that modus ponens cannot be justified to someone who is not already prepared to use that rule.