 Theist faith as assent to truths on the basis of an authoritative source of divine revelation is possible, though, only for those who already believe that God exists and is revealed through the relevant sources. Might such faith, then, have to rest on a prior faith—faith that God exists and that this is God’s messenger or vehicle of communication? Those foundational claims, it might be maintained, are held true on the grounds of adequately supporting evidence, such as putatively provided by arguments of natural theology and the claimed evidence for miraculous endorsement of a prophet’s authority. Theist faith might then have a purely rational foundation. But this could hardly be so for every person of faith, since not everyone who believes will have access to the relevant evidence or be able to assess it properly. Besides, and more importantly, although Aquinas allows that rational assessment of the available evidence may lead a person to faith, he does not think that such an assessment could ever elicit assent itself—only demonstration could achieve that and so high a level of proof is not here available (see Aquinas [2006], footnote 2b, 58–9). Aquinas’s view is thus that all believers stand in need of God’s grace: ‘the assent of faith, which is its principal act … has as its cause God, moving us inwardly through grace’ (Summa Theologiae, 2a2ae 6, 1 (Aquinas [2006], 167)). It follows, then, that, on Aquinas’s view, believing that God exists and is revealed in specific ways is itself a matter of faith, and not a purely rationally evidentially secured prolegomenon to it.