"But let us never forget, either, as all conventional history of philosophy conspires to make us forget, what the 'great thinkers' really are: proper objects, indeed, of pity, but even more, of horror."
David Stove's "What Is Wrong With Our Thoughts" is a critique of philosophy that I can only call epic.
The astute reader will of course find themselves objecting to Stove's notion that we should be catologuing every possible way to do philosophy wrong. It's not like there's some originally pure mode of thought, being tainted by only a small library of poisons. It's just that there are exponentially more possible crazy thoughts than sane thoughts, c.f. entropy.
But Stove's list of 39 different classic crazinesses applied to the number three is absolute pure epic gold. (Scroll down about halfway through if you want to jump there directly.)
I especially like #8: "There is an integer between two and four, but it is not three, and its true name and nature are not to be revealed."
Possibly Stove intended this only as an extended Take That to philosophers he dislikes; but it seems to me that he is a bit too dismissive of his own project, the 'nosology'. Without wanting a Fully General Counterargument, I think it might be useful to have a set of, say, five or six different classes of erroneous statements; and I also think Stove is too eager to insist on the singularity of each of his examples. For example, he states that the objection "not verifiable" cannot be applied to his example 8; I don't see why not. Anything whose "name and nature are not to be revealed" has just been declared unverifiable, no? Similarly 3 through 7 look pretty unverifiable to me.
Then he has some examples further down the list which look reasonably testable, such as 13 : "3 is a lucky number". One could easily do an experiment on this by submitting lottery tickets with and without 3's filled in; and as for 14, I think a simple "false-to-fact" would suffice to dismiss it.
So far then there are three classifications: False to fact, contradiction, meaningless through having no connection to observation. We may need a fourth to cover such statements as 26: "The tie which unites the number three to its properties (such as primeness) is inexplicable". This seems somehow vaguely related to observation, in that there does seem to be something called three which has the property of primeness, and nobody has really explained the tie between triples of objects and these properties. (It is perhaps not strongly coupled to observation, but I hesitate to dismiss it completely on that ground.) I suggest a fourth classification of 'uninteresting' or 'unfruitful': A proposition which, when adopted as an axiom, yields few or no deductions, is unfruitful. One might also call it the 'So What' error: Making statements which even if true are not useful to know.
There does seem to be some overlap here; for example, Stove's 25: "Five is of the same substance as three, co-eternal with three, very three of three: it is only in their attributes that three and five are different." This looks to me quite unverifiable, but even if it were true, So What? What conclusions or prediction would you draw from this?
Contrary to Stove, I think these four will cover all his list: False to fact, contradiction, meaningless, and So What. I am not certain, however, whether this insight is useful.
I'd unify your "So What" with "meaningless" into a single category "does not constrain observations". Math passes the test inasmuch as it constrains observations about outcomes of proof checking.
But now some people will complain (are already complaining) that we reject the majority of humanity's thought.