(1843) Critique of Hegel's philosophy of right
“The weapon of criticism cannot, of course, replace criticism of the weapon, material force must be overthrown by material force; but theory also becomes a material force as soon as it has gripped the masses.”
(1867) Capital, vol. I
“There is no royal road to science, and only those who do not dread the fatiguing climb of its steep paths have a chance of gaining its luminous summits.”
“My dialectic method is not only different from the Hegelian, but is its direct opposite. To Hegel, the life process of the human brain, i.e., the process of thinking, which, under the name of “the Idea,” he even transforms into an independent subject, is the demiurgos of the real world, and the real world is only the external, phenomenal form of “the Idea.” With me, on the contrary, the ideal is nothing else than the material world reflected by the human mind, and translated into forms of thought.”