The reconciliation of faith and reason was the dominant concern of John Henry Cardinal Newman's intellectual life. His fifteen "University Sermons" show him wrestling with the subject throughout his twenty years as an Anglican cleric. In An Essay in Aid of a Grammar of Assent, written after his conversion to Roman Catholicism, Newman forged his thought on the subject into a more coherent whole.
Newman insisted that the human ratiocinative faculty depends, to a greater degree than was at the time appreciated, on assumptions and inferences which cannot be put into words. Rationality, in his view, was "any process or act of the mind, by which, from knowing one thing, [the mind] advances on to know another." This definition of rationality positioned him to argue that certainty in religious belief was as "reasonable" as many of the non-religious beliefs accepted with certainty by every normal mind in the course of everyday life. Newman sought to show that as in non-religious matters, so in Christian faith, a person may reasonably believe propositions she cannot prove to be true.
"Cardinal Newman and Jury Verdicts: Reason, Belief, and Certitude,"
Yale Journal of Law & the Humanities: Vol. 8
, Article 4.
Available at: https://digitalcommons.law.yale.edu/yjlh/vol8/iss1/4