Theory that bases scientific knowledge on the separation between "objective" facts - supposedly external to thought - and "subjective" analysis, supposedly proper to the individual mind. As the subjective is individual, the universalization of results requires either a metaphysical confusion between the facts themselves and the concepts or categories with which they are described or in which they are grouped, or else accepting the impossibility of a theoretical universalization of empirical results without a prior approach to the totality.
Marxist critique of empiricism
By starting from a fracture of reality between the objective - supposedly natural - and the subjective - supposedly individual - empiricism creates its own dead end.
When one gets used to assigning a certain kind of reality, outside our mind, to √-1 or to the fourth dimension, it no longer matters much if one goes a step further and also accepts the spirit world of the mediums.
Frederick Engels. Natural Science in the Spirit World, 1878
The "exteriority" of one part of reality with respect to another makes it impossible to affirm a reality, and therefore a theory capable of explaining it in all its interrelations simultaneously. This is the basis of the impossibility of developing a "complexity theory", or even a more modest "systems theory", from the empiricist epistemology.
However great the contempt for all theoretical thought may be, without it one cannot relate two natural facts to each other or penetrate the connection that exists between them. The only question is whether the thinking is correct or not, and there is no doubt that disdain for theory is the surest way to think naturalistically and, therefore, falsely.
Frederick Engels. Natural Science in the Spirit World, 1878
The initial dualism of empiricism translates into its own historical dichotomy: either it has to start from abstractions and concepts ex ante, which it can only link arbitrarily to the very experience supposedly "analyzed" a posteriori...
It is the old story. First all sensory things are turned into abstractions, and then one wants to know them by means of the senses, to see time and smell space. The empiricist becomes so steeped in the habit of empirical experience that he believes he is still in the field of sensory experience when he is working with abstractions.
Frederick Engels. Dialectics of Nature.
...Or else it becomes a casuistry that has to give up any claim to universal knowledge, paralyzed by the empirical possibility of its refutation.
We have seen that the starting point and fundamental premise of the philosophy of empirio-criticism is subjective idealism. The world is our sensation: such is the fundamental premise, veiled, but in no way modified by the little word "element" and by the theories of the "independent series", of "coordination" and of "introjection". The absurdity of this philosophy is that it leads to solipsism, to the recognition that only the philosophizing individual exists.
Lenin. Materialism and Empirio-criticism, 1908.
The final form of empiricism ends up twisting into a world where "methodological solipsism" goes from being a scientific premise to reigning over an increasingly divided society.
As long as each one of the alleged miracles has not been explained, they still have enough room to carry on.
Frederick Engels. Natural Science in the Spirit World, 1878
That is to say, empiricism can only overcome the artificial fracture it presupposes in reality through metaphysics, or else turn into the most brutal relativism. That is why the opposition "modernity-postmodernity" is not really one, but a consequence, present from its very origins, of the bourgeoisie's approach to knowledge.