The Second Vatican Council positively asserts that it is possible for the non- Christian to attain salvation, though at the same time it declares that such salvation is achieved in ways that are known to God alone. In a tacit but noteworthy correction to the officially received theology which had hitherto been more or less unanimous on this point, it was declared at the Second Vatican Council that atheists too are not excluded from this possibility of salvation, though here the distinctions between positive and negative atheism, between atheism of greater or lesser duration, usually accepted up to that point were not applied at the Second Vatican Council. The only necessary condition which is recognized here is the necessity of faithfulness and obedience to the individual's own personal conscience. This optimism concerning salvation appears to me one of the most noteworthy results of the Second Vatican Council. For when we consider the officially received theology concerning all these questions, which was more or less traditional right down to the Second Vatican Council, we can only wonder how few controversies arose during the Council with regard to these assertions of optimism concerning salvation, and wonder too at how little opposition the conservative wing of the Council brought to bear on this point, how all this took place without any setting of the stage or any great stir even though this doctrine marked a far more decisive phase in the development of the Church's conscious awareness of her faith than, for instance, the doctrine of collegiality in the Church, the relationship between scripture and tradition, the acceptance of the new exegesis etc. 

Problem of the "Anonymous Christian", Theological Investigations, Vol. 14