Schopenhauer on Hegel: "A flat-headed, insipid, nauseating, illiterate charlatan."
There's nothing like a good insult or two, and if you're looking for insults in philosophy, you need look no further than Arthur Schopenhauer's comments on his German contemporary, the much more popular and successful Friedrich Hegel.
Schopenhauer suggested as a motto of Hegel’s philosophy some words of Shakespeare: ‘such stuff as madmen tongue and brain not’.
"Hegel, installed from above, by the powers that be, as the certified Great Philosopher, was a flat-headed, insipid, nauseating, illiterate charlatan, who reached the pinnacle of audacity in scribbling together and dishing up the craziest mystifying nonsense. This nonsense has been noisily proclaimed as immortal wisdom by mercenary followers and readily accepted as such by all fools, who thus joined into as perfect a chorus of admiration as had ever been heard before. The extensive field of spiritual influence with which Hegel was furnished by those in power has enabled him to achieve the intellectual corruption of a whole generation."
Schopenhauer, who basically regarded Hegel as a paid agent of the Prussian dictatorship of that time, wasn't exactly perfection incarnate himself, and served up some nonsense of his own. For example, his essay 'On Women' shows himself up as a pretty disgraceful misogynist (something which was apparently inspired by his relationship to his mother). He was also driven by resentment at Hegel's worldly success and his own lack of, since for most of his life his writings, and especially his great work The World as Will and Representation, were completely ignored.
Karl Popper, who invokes the above words during his own attack on Hegel in The Open Society and Its Enemies, calls Schopenhauer: "a Platonic idealist and a conservative if not a reactionary, but a man of supreme integrity who cherished truth beyond anything else. There can be no doubt that he was as competent a judge in philosophical matters as could be found at the time."
In his own attack on Hegel, Popper says:
"Hegel’s intention is to operate freely with all contradictions. ‘All things are contradictory in themselves’, he insists, in order to defend a position which means the end not only of all science, but of all rational argument. And the reason why he wishes to admit contradictions is that he wants to stop rational argument, and with it scientific and intellectual progress. By making argument and criticism impossible, he intends to make his own philosophy proof against all criticism, so that it may establish itself as a reinforced dogmatism, secure from every attack, and the insurmountable summit of all philosophical development."
Both Schopenhauer and Popper make important points which are still relevant today, with ideological politics very much retaining their allure, for example in Islamism and forms of feminism that invoke unchanging social structures (for more on this see my series on Karl Popper and the fight against ideological nonsense)