has given a very close account of his progress from atheism to theism. Every point along this path was marked by an attention to the rational arguments pro and contra the existence of God and he asserts that Thomistic arguments rightly understood were decisive in his conversion. This notion of right understanding is critical. Can one have a right understanding of the argument eg. The Third Way, and still not be persuaded or is your not being persuaded an indication that you do not have the right understanding that you think you have. Though he is not explicit on this point this implication seems ineluctable, the ineluctable modality of the intelligible as it were.
So then at a certain point, the argument, rightly understood, became the irresistible force which pushed him over the line into theism specifically into Catholic Christianity. In this very rational progress he is to be contrasted to Saint Augustine who wobbled his way to faith via the felt insufficiency of various universal schemas. Mystical experience and grace played a major part in his conversion. No one doubts that he was smart enough to get the most powerful Christian theistic arguments of the day but for Augustine to forgo the pleasures of the flesh he had to really know in the flesh. Professor Feser does admit to the guidance of the Holy Spirit during his period of seeking but he also says that once having arrived he had arrived and the proofs of the existence of God do not require the assistance of the Holy Spirit to be accepted.
Do I think that the Holy Spirit was guiding me when I came to see God's existence, etc.? Absolutely. Did that play (and does it play now) any role in my reasons for believing in God? Absolutely not. If someone wants to know why I think God exists, they can read my various writings defending the arguments for God's existence, because those are my reasons. I wouldn't say to them "Oh, and also I've got this experience of the Holy Spirit." That's got nothing to do with it.
The question I have to ask and it is one which can be relevant to many philosophical problems: Can one understand an argument in all its detail and yet not feel the force of its conclusion? The answer to that must be yes because it is a common experience and if someone said to you - you’re only saying that because you haven’t rightly understood the argument, the only answer would be a giant shrug.