How did An Essay in Aid of a Grammar of Assent explain religious faith and certainty?

In An Essay in Aid of a Grammar of Assent, published in 1870, St. John Henry Newman explores the nature of religious faith and the mechanism by which it achieves certainty.1

Newman addresses the philosophical challenge of how an individual can arrive at absolute certainty regarding religious truths when the underlying evidence is often merely probable rather than demonstrably certain. He argues that faith is not solely dependent on formal, logical proofs, but rather involves a complex process of personal conviction that allows the mind to move from probable evidence to a state of firm, certain assent. By examining the psychology of belief, Newman seeks to demonstrate that such certainty is a rational and valid response to the cumulative weight of evidence, even when that evidence falls short of mathematical or scientific proof.1