 In his 1947 “What is Cantor’s Continuum Problem?”, Gödel expounds the view that in the case of meaningful propositions of mathematics, there is always a fact of the matter to be decided in a yes or no fashion. This is a direct consequence of realism, for if there exists a domain of mathematical objects or concepts, then any meaningful proposition concerning them must be either true or  false.[23]  The Continuum Hypothesis is Gödel’s example of a meaningful question. The concept “how many” leads “unambiguously” to a definite meaning of the hypothesis, and therefore it should be decidable—at least in principle. Most strikingly Gödel does not leave the matter there but goes on to offer a practical strategy for determining the value of the continuum, as well as the truth value of other axioms extending ZFC. Specifically, he offers two criteria for their decidability: the first involves conceptual analysis and is associated with Gödel’s rationalistic program. (See the above section on Gödel’s rationalism.) Secondly one must keep an eye on the so-called success of the axiom, as a check or indicator of which direction to look to for the solution of its truth. For example, Gödel notes in the paper that none of the consequences of the Axiom of Constructibility are very plausible. It is, then, likely false. See Maddy 2011 and Koellner 2014 for discussion of intrinsic vs extrinsic justifications for new axioms of set theory.