What does "subtle wisdom" mean?

Question

I've always understood subtle to mean the opposite of obvious, as in subtle difference, until I came across this line from The Duchess of Malfi

Oh, sir, the opinion of wisdom is a foul tetter that runs all over a dead man's body. If simplicity direct us to have no evil, it directs us to a happy being. For the subtlest folly proceeds from the subtlest wisdom.

I had to revisit a dictionary to check for other possible meanings because I couldn't make any sense of wisdom that's barely noticeable. Now it seems to me that subtle here is used in two different meanings: subtle folly is folly that can barely be seen, and subtle wisdom is wisdom that's deep and penetrative. So, the way I understand the sentence is if you have deep wisdom, you're least likely to experience folly, and vice versa. How correct am I?

Edit:

The Webster dictionary has this one sense among others for subtle:

Having or marked by keen insight and ability to penetrate deeply and thoroughly: a subtle scholar.

So I thought this was probably the right sense for subtle wisdom. Then I ran a google search with "his subtle wisdom" (with quotes), and finally landed on the following quote from this website:

The premise for each episode was simple, Barry Livingston says. “The boys have a problem, and MacMurray, with his subtle wisdom, lets them work it out—but guides them with an invisible hand.”

Answer 1

This play was written in 1612, and uses archaic language. If you're going to read literature written in older English, you must consult dictionaries that include older meanings of words:

subtle (adj): 3. archaic Crafty; cunning

To properly interpret it in this context, it helps to include more of the scene:

ANTONIO. Now, sir, in your contemplation? You are studying to become a great wise fellow.

BOSOLA. O, sir, the opinion of wisdom is a foul tetter that runs all over a man’s body: if simplicity direct us to have no evil, it directs us to a happy being; for the subtlest folly proceeds from the subtlest wisdom: let me be simply honest.

ANT. I do understand your inside.

BOS. Do you so?

ANT. Because you would not seem to appear to th’ world; Puff’d up with your preferment, you continue; This out-of-fashion melancholy: leave it, leave it.

BOS. Give me leave to be honest in any phrase, in any compliment whatsoever. Shall I confess myself to you? I look no higher than I can reach: they are the gods that must ride on winged horses. A lawyer’s mule of a slow pace will both suit my disposition and business; for, mark me, when a man’s mind rides faster than his horse can gallop, they quickly both tire.

Bosola claims that he is not an usually wise or perceptive person, that he has modest ambitions and does not wish to think too deeply or to worry about having a quick wit -- in short that he merely wants to be "simply honest". In this context "the subtlest folly proceeds from the subtlest wisdom" is simply a warning that a man should not be too clever, as in the similar contemporary expression

You are too clever for your own good.

or

You are too clever by half.

However in the full context of the play Bosola is putting on a false front, as he is actually the agent of the Duchess' brothers, sent to spy on her and her husband Antonio. He ingratiates himself with Antonio in order to gain his confidence, which later he uses to expose them.

Answer 2

I am going to collate the comments I made under the question itself into an answer.

I don't see the meaning of "subtlest folly" or "subtlest wisdom" as being different from the opposite of obvious. In other words, I still see such things to be taken as "almost undetectable."

In the sense "having or marked by keen insight and ability to penetrate deeply and thoroughly," and the example of "subtle scholars," that still doesn't mean that something is obvious.

In fact, scholars who are not subtle will likely not understand how subtle scholars reach the conclusions they do (barring detailed explanations). Here, subtle means something more like nuanced or discerning. The scholars are described as subtle because they are able to see things that other people can't. In short, it's the scholars who are "deep and penetrative," not the knowledge (wisdom) that they gain or apply. You might call them "scholars of subtlety."

But it's not a contradiction to say that knowledge can be both deep and difficult for others to detect at the same time.

For instance, "God acts in mysterious ways" could be paraphrased as "God is subtle." In other words, all of existence is influenced (it's a deep influence)—but nobody understands what the the purpose of that influence is (it's also difficult to detect).

Answer 3

I think "easy to miss" or "difficult to detect" is a better description of the meaning of the word "subtle" than "barely noticeable," as the latter kind of implies a lack of significance, which may be far from the case.

"Subtle wisdom": An easy to miss but potentially important action taken or thought conveyed which reflects a capacity or a propensity to come to correct conclusions or make choices that anticipate and avoid problems and/or propel toward desirable outcomes.

Example: "Her expression conveyed objection but betrayed no malice. This subtle wisdom earned her a momentary regard."