(These are excerpts. You can read the entire argument here.)
The question of method in moral reasoning has a long and heavy history. Beginning with Ockham (Nominalism), exacerbated by Descartes (Rationalism), and even more by Kant (his ‘Copernican revolution in philosophy’), our concept of ‘reason’ has been increasingly separated from experience and narrowed to something more and more resembling what computers do. The Aristotelian and Thomistic (and, more generally, pre-modern) meaning of ‘reason’ is broader. It had to be, to justify the definition of man as ‘the rational animal.’ It included the immediate, intuitive understanding (‘the first act of the mind’ in Aristotelian-Scholastic logic) and intuitive judgment (‘the second act of the mind’) as well as inductive or deductive reasoning (‘the third act of the mind’).
It's useful to recall that "ordering" is important, so "first, second, and third" denote (to some extent) the right-ordering of 'reason' in the Ari/Thomist tradition. IOW, "immediate, intuitive, reasoning" is more weighty to Ari/Thom than is "inductive/deductive".
We moderns have narrowed ‘intuition’ as we have narrowed ‘reason,’ so that ‘intuition’ now means ‘irrational feeling.’ ‘Intuitive reason’ or ‘rational intuition’ sounds to us like an oxymoron. When we read Pascal’s famous saying that ‘the heart has its reasons, that the reason does not know,’ we think he is exalting something else against reason, when he is saying exactly the opposite: that the heart, the faculty of immediate intuition, has reasons. It sees. It has eyes. It is a crucial part of ‘reason.’...Thus we no longer see ‘moral intuition’ or its application to our moral judgment of concrete situations like Live Action’s ‘sting’ as part of ‘reason,’ as Aristotle, Augustine, and Aquinas did. (Aquinas called this moral intuition ‘synderesis.’)
This is not simply a case of altered conventional usage, but of real error. Since we are not angels, all our knowledge begins with experience, and our moral knowledge begins with moral experience—experience of concrete cases. Before we reason about these (by ‘ratio,’ the ‘third act of the mind’), we understand them (by ‘intellectus,’ the ‘first act of the mind’) and judge them (the ‘second act of the mind’) by the ‘habit’ of moral judgment. In other words, we begin with the concrete, not with the abstract. Only after experience do we rise to the level of abstractions...
Immediately following that, Kreeft demolishes "Symbolic Logic"--which was inflicted on Phil 101 students at Marquette U a few decades ago, despite the evident distaste for the course by MU's Chair/Philosophy at the time.
Another wonderful digression:
When morally sane human beings hear the very clever and intelligent arguments of a philosopher like Peter Singer for ascribing more rights to whales than to babies and no more importance to your own family than to anyone else, they do not begin by looking for his logical mistakes. They say something like: “That idea is so stupid that you have to have a Ph.D. to believe it.” They have moral common sense.
And: any argument that begins by contradicting our moral common sense is almost certainly going to be wrong
Read the whole thing. It's worthwhile.