The validity of an argument means only that it is logically impossible for its premisses to be true and its conclusion false. And this means only that it is logically necessary that either one or more [of] its premises are false or its conclusion is true … A valid argument is not so much a proof as a choice. It presents the critical thinker with a set of mutually exclusive alternatives between which he must choose. He can choose either to accept the premisses of the argument, in which case he must also accept its conclusion; or to reject (or suspend judgment concerning) the premisses of the argument, in which case he need[s] do nothing at all vis-à-vis its conclusion. The critical thinker can decide to do any of these things. But the work of the argument is to show him that he cannot, without contradicting himself, choose to both accept its premises and reject its conclusion. (pp. 133-134)
Notturno, M. A. (2000). Science and the open society: The future of Karl Popper’s philosophy. Budapest: Central European Univeristy Press.