As traditionally understood, faith rests on an interior illumination which makes the believer certain that the doctrine proposed for belief is true. St Thomas calls this illumination ‘the light of faith’, and Calvin, ‘the interior testimony of the Holy Spirit.’ The claim of certainty encounters some serious difficulties, however, and it seems tome we have to accept an interpretation of the ‘light of faith’ in which some doubts are left unresolved. Faith turns out not to be a simple state at all, but is composed of three distinct elements. The first element is an intuition that what is proposed for belief is true, which is accompanied by hesitation and fear of error. The second element is the infusion of a doubt-free state, in which doubts, while not resolved, are removed to the periphery of consciousness, and lose their power to cause anxiety. The third element is an intuition which makes the believer certain that he is morally required to allow this state to continue. Although many of the sources I will be discussing use ‘faith’ in an exclusively Christiansense, I believe my conclusions will hold for theistic faith in general.