In the Introduction you have the criticism, first (Par. 26, etc.) of Wolf's version of Leibnitz (metaphysics in the historical sense), then of English-French empiricism (par. 37, etc.) then Kant (par. 40, seq.) and finally (par. 61) of Jacoby's mysticism. In the first section (Being) do not spend too long over Being and Nothing; the last paragraphs on Quality and then Quantity and Measure are much finer, but the theory of Essence is the main thing: the resolution of the abstract contradictions into their own instability, where one no sooner tries to hold on to one side alone than it is transformed unnoticed into the other, etc. At the same time you can always make the thing clear to yourself by concrete examples; for instance, you, as a bridegroom, have a striking example of the inseparability of identity and difference in yourself and your bride. It is absolutely impossible to decide whether sexual love is pleasure in the identity in difference or in the difference in identity. Take away the difference (in this case of sex) or the identity (the human nature of both) and what have you got left? I remember how much this very inseparability of identity and difference worried me at first, although we can never take a step without stumbling upon it. But you ought on no account to read Hegel as Herr Barth has done, namely in order to discover the bad syllogisms and rotten dodges which served him as levers in construction. That is pure schoolboy's work. It is much more important to discover the truth and the genius which lie beneath the false form and within the artificial connections. Thus the transitions from one category or from one contradiction to the next are nearly always arbitrary often made through a pun, as when Positive and Negative (Par. 120) "zugrunde gehen" [perish] in order that Hegel may arrive at the category of "Grund" [reason, ground]. To ponder over this much is waste of time. Since with Hegel every category represents a stage in the history of philosophy (as he generally indicates), you would do well to compare the lectures on the history of philosophy (one of his most brilliant works). As relaxation, I can recommend the sthetic. When you have worked yourself into that a bit you will be amazed. Hegel's dialectic is upside down because it is supposed to be the "self-development of thought," of which the dialectic of facts therefore is only a reflection, whereas really the dialectic in our heads is only the reflection of the actual development which is fulfilled in the world of nature and of human history in obedience to dialectical forms. If you just compare the development of the commodity into capital in Marx with the development from Being to Essence in Hegel, you will get quite a good parallel for the concrete development which results from facts; there you have the abstract construction, in which the most brilliant ideas and often very important transmutations, like that of quality into quantity and vice versa, are reduced to the apparent self-development of one concept from another one could have manufactured a dozen more of the same kind.
Letters: Marx-Engels Correspondence 1891