Marx's passage about
The Mystery of Idealist Speculation in The Holy Family, 1844 :

"If from real apples, pears, strawberries and almonds I form the general idea "Fruit”, if I go further and imagine that my abstract idea "Fruit”, derived from real fruit, is an entity existing outside me, is indeed the true essence of the pear, the apple, etc., then in the language of speculative philosophy — I am declaring that "Fruit” is the "Substance” of the pear, the apple, the almond, etc. I am saying, therefore, that to be a pear is not essential to the pear, that to be an apple is not essential to the apple; that what is essential to these things is not their real existence, perceptible to the senses, but the essence that I have abstracted from them and then foisted on them, the essence of my idea — "Fruit”. I therefore declare apples, pears, almonds, etc., to be mere forms of existence, modi, of "Fruit” My finite understanding supported by my senses does of course distinguish an apple from a pear and a pear from an almond, but my speculative reason declares these sensuous differences inessential and irrelevant. It sees in the apple the same as in the pear, and in the pear the same as in the almond, namely "Fruit”. Particular real fruits are no more than semblances whose true essence is "the substance" — "Fruit”.

(...) Having reduced the different real fruits to the one "fruit" of abstraction — "the Fruit", speculation must, in order to attain some semblance of real content, try somehow to find its way back from "the Fruit", from the Substance to the diverse, ordinary real fruits, the pear, the apple, the almond, etc. 


The speculative philosopher therefore relinquishes the abstraction "the Fruit", but in a speculative, mystical fashion — with the appearance of not relinquishing it. Thus it is really only in appearance that he rises above his abstraction.


The different ordinary fruits are different manifestations of the life of the "one Fruit"; they are crystallisations of "the Fruit" itself. Thus in the apple "the Fruit" gives itself an apple-like existence, in the pear a pear-like existence.


Thus "the Fruit" is no longer an empty undifferentiated unity; it is oneness as allness, as "totality” of fruits, which constitute an "organically linked series of members”. In every member of that series "the Fruit" gives itself a more developed, more explicit existence, until finally, as the "summary” of all fruits, it is at the same time the living unity which contains all those fruits dissolved in itself just as it produces them from within itself (...).


Hence what is delightful in this speculation is to rediscover all the real fruits there, but as fruits which have a higher mystical significance, which have grown out of the ether of your brain and not out of the material earth, which are incarnations of "the Fruit", of the Absolute Subject. (...) Your main interest is then to point out the unity of "the Fruit" in all the manifestations of its life — the apple, the pear, the almond — that is, to show the mystical interconnection between these fruits, how in each one of them "the Fruit" realises itself by degrees and necessarily progresses, for instance, from its existence as a raisin to its existence as an almond. Hence the value of the ordinary fruits no longer consists in their natural qualities, but in their speculative quality, which gives each of them a definite place in the life-process of "the Absolute Fruit"


The ordinary man does not think he is saying anything extraordinary when he states that there are apples and pears. But when the philosopher expresses their existence in the speculative way he says something extraordinary. He performs a miracle by producing the real natural objects, the apple, the pear, etc., out of the unreal creation of the mind "the Fruit", i.e., by creating those fruits out of his own abstract reason, which he considers as an Absolute Subject outside himself, represented here as "the Fruit". And in regard to every object the existence of which he expresses, he accomplishes an act of creation.

It goes without saying that the speculative philosopher accomplishes this continuous creation only by presenting universally known qualities of the apple, the pear, etc., which exist in reality, as determining features invented by him, by giving the names of the real things to what abstract reason alone can create, to abstract formulas of reason, finally, by declaring his own activity, by which he passes from the idea of an apple to the idea of a pear, to be the self-activity of the Absolute Subject, "the Fruit"

In the speculative way of speaking, this operation is called comprehending Substance as Subject, as an inner process, as an Absolute Person, and this comprehension constitutes the essential character of Hegel's method.

(The Holy Family, ch.5, http://www.marxist.org)

Internal Fraction of ICC - Communist Bulletin (Nš 39)