After having this rather expensive "real practicing philosopher" book on my shelf for a long time partially read, I have finally finished the rather herculean task of completing it, although it is doubtful I will ever reach the ennobled state of claiming significant understanding of it in this mortal coil. The complexity, arcane technicalities of lexical analysis and obscurantism of thought that philosophy is drawn to never ceases to amaze me.
Let me TRY to make this somewhat simple.
The purpose of the book is to cover the various "assaults on reason" from the start of philosophy up to the present. One can validly call that "assaults on transcendence", which in it's easiest to understand form is "God" ... and especially the particularly rational form of God introduced in the canon of Western Christianity.
To give the form of the problem, I think Mannheim does a good job:
"one must make one's choice between two views: on the one hand that there is a reason working in and through men's minds which can lay hold of a timeless structure of things: on the other, that thinking is a series of temporal events determined, like all other events, non-rationally"In other words, reason vs positivism. Reason (in it's most productive historical use) says roughly "there is a grand plan, and it is discoverable because our minds happen to be made to relate to that grand plan". Positivism says there is no plan, only a pile of "events" with no "privileged frame of reference", certainly including our concepts of "reason", "meaning", etc.
Naturally, Mannheim liked the non-transcendent view, but wanted to make it privileged ... which of course is immediately self-refuting as is all relativism, since there IS NO PRIVILEGED (eg "right", "better", etc) POINT OF VIEW ... if there aren't any universals, absolutes, etc, there can't be.
Or to put it another way in roughly the terms of Heidegger:
"As the existentialist contemplated this world, his feeling was one of nausea. Was there anything in this nightmare that he could tie to? One thing only - his own existence. Certain of nothing else, he could be certain at least that he existed, and that he was somehow fashioning his own fate. And in doing so, his safety lay in the depth of his disillusionment. He was weak; he was a pilgrim and stranger in a world not of his making; he would be defeated shortly by death; there were no principles that he could adhere to; his life therefore was to be one of anxiety and care. But for Heidegger, "deliverance from illusion is to be achieved by the man, who, opening himself to anguish, resolutely faces nothingness in anticipation of his own extinction"".Hard to beat that as an upbeat recruitment paragraph for "Life without God, The Nietzschean way".
As is pointed out in the rest of the book in number of places, most philosophers in attacking reason, causality, universals, etc and attempting to replace them with mathematics, logical atomism, category differences, and a host of other chimeras, are actually unable to practice what they preach in order to even make the attempt. They are forced to use reason, causality, universals, etc in order to even get a running start at their attack.
"I attack the principle of solid ground while standing here on .... er, never mind". Only they fail to realize their predicament.
Needless to say, it gets quite hard to keep an open mind about the usefulness of all this after the first 10 or so attempts that always must be arrogantly and loudly launched -- after all, if one is to rush as Quixote to the windmill of all of human thought for thousands of years, as well as the day to day existence experienced by ones own self and all those of one's shared existence to date, one must have a quite high opinion of their own logic -- er "series of temporal brain events".
And so it goes. The vast vast majority of even all somewhat deep thinkers either fail to, or more likely refuse to, consider the difficulty factor of doing away with little basics like a rational repeatable universe that is understandable to themselves and others in the same manner taken as a "universal a priori fact". What they see as a "problem" is of course that such a universal a priori fact is hard to accept without some cause beyond "shit happens", and is perilously close to "God".
Much as in Mannheim's choice "You have to face the fact that there is a God, or there isn't", many like to jump to "there isn't" in hopes of being freed from moral stricture and eventual judgement, but like Mannheim, completely ignore the existential consequence of the no god, no order, no universals, no reason for there to be reason, meaning, etc. The abyss of despair.
The previous paragraph is the reason that I think having some understanding of how philosophy, or at least epistemology works is important and a major area of lack in modern western education.
Ideas do indeed have consequences.