The definitions of "reason" and "unreason" remain a subject of wide-ranging philosophical and psychological debate; the nature of human thought and consciousness is a very large discussion, indeed, and one that I didn't really wish to wade into. I thus opted for wisdom and foolishness, which speak not so directly of a presence or absence of reason, but of polar qualities of it. Wisdom would be reason of the highest quality; foolishness of the lowest, which by virtue of its poor quality would be very nearly a lack of reason, to wit: unreason. So, while Mr. Mitchell might well engage me further on my specific choice of terms, I don't think them ill-suited to my purpose.
Also, he was speaking only of his own mind, rather than the minds of “all men.”
Ah, I was fooled by his final declaration: "And the same is true of you, and of each of us." I took him rather literally, I'm afraid.
Are people with a serious mental illness never capable of using reason?
I would say that, yes, some are truly incapable, but not all. I have had experiences with deranged persons having lucid moments, and as you have noted, they can sometimes speak quite sensibly. Still, there are those tragic souls who have no lucid moments. May God grant them eternal mercy.
I think I'm following this. "Wit and Wisdom" are often paired and compared, while foolishness would be to wit, unreason.
And therefor, by interpolation: The vaunted political characteristic of compromise would correspond to half-wittedness.
If (as Mr. Mitchell does) we describe “reason” as the capacity to analyze one’s own thoughts, to examine their correspondence to reality, and to seek greater understanding of our own minds, then I would say that there are very few who are not capable of reason, however rarely they exercise it. “Unreason,” the failure to attempt the process of determining truth, can indeed be said to be behind a great deal of harm. If a person fervently believes, and vigorously acts upon, beliefs that are false, we do end up, among other problems, Hitler. And Barack Obama.
Consider the idea that voting for a candidate with a dark-skinned African father “proves” that the voter is not racist. Obviously, this idea doesn’t stand up to rational consideration for a moment, since the very definition of “racist” is “making decisions based on outward signs of genetic heritage.” Is doing what we imagine is good for the “black” person - such as electing him president, or admitting him, unqualified, to Harvard Law - any less racist than doing something obviously bad, such as beating him up or forcing him to do farm labor? This demonstrates the real danger of Unreason, because the same false belief, acted upon to produce “warm feelings in the belly,” can have results ranging from apparently positive to obviously disastrous.
Mr. Mitchell posits, and I tend to agree, that anyone capable of using language consciously is capable of exercising reason, at some times and to some extent. This would leave out the catastrophically insane and very young children. (Pat can reason, James - maybe, Vlad really isn’t although he talks up a hurricane.) The extent to which each person uses reason depends on both internal and external factors unique to the person.