Die Religion ist der Seufzer der bedrängten Kreatur, das Gemüt einer herzlosen Welt, wie sie der Geist geistloser Zustände ist. Sie ist das Opium des Volks. Die Aufhebung der Religion als des illusorischen Glücks des Volks ist die Forderung seines wirklichen Glücks.
Religion is the sigh of the oppressed creature, the heart of a heartless world, just as it is the spirit of spiritless conditions. It is the opium of the people. To abolish religion as the illusory happiness of the people is to demand their real happiness.

A specter is haunting Europe—the specter of Communism. All the Powers of old Europe have entered into a holy alliance to exorcise this specter: Pope and Czar, Metternich and Guizot, French Radicals and German police-spies.

Darwin has interested us in the history of nature’s technology.

Darwin’s book is very important and serves me as a basis in natural science for the class struggle in history. One has to put up with the crude English method of development, of course. Despite all deficiencies not only is the death-blow dealt here for the first time to “teleology” in the natural sciences, but their rational meaning is empirically explained.

In our days everything seems pregnant with its contrary. Machinery, gifted with the wonderful power of shortening and fructifying human labor, we behold starving and overworking it… . At the same pace that mankind masters nature, man seems to become enslaved to other men or his own infamy. Even the pure light of science seems unable to shine but on the dark background of ignorance.

Life is not determined by consciousness, but consciousness by life.

Mankind always takes up only such problems as it can solve; since, looking at the matter more closely, we will always find that the problem itself arises only when the material conditions necessary for its solution already exist or are at least in the process of formation.

Medicines heals doubts as well as diseases.

Men make their own history, but not just as they please. They do not choose the circumstances for themselves, but have to work upon circumstances as they find them, have to fashion the material handed down by the past. The legacy of the dead generations weighs like an alp upon the brains of the living.

Natural science will in time incorporate into itself the science of man, just as the science of man will incorporate into itself natural science: there will be one science.

So far no chemist has ever discovered exchange-value either in a pearl or a diamond.

Social relations are closely bound up with productive forces. In acquiring new productive forces men change their mode of production; and in changing their mode of production, in changing the way of earning their living, they change all their social relations. The hand-mill gives you society with the feudal lord; the steam-mill, society with the industrial capitalist.

The development of civilization and industry in general has always shown itself so active in the destruction of forests that everything that has been done for their conservation and production is completely insignificant in comparison.

The philosophers have only interpreted the world in various ways, the point is to change it.

The product of mental labor—science—always stands far below its value, because the labor-time necessary to reproduce it has no relation at all to the labor-time required for its original production.

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.

We know only a single science, the science of history. History can be contemplated from two sides, it can be divided into the history of nature and the history of mankind. However, the two sides are not to be divided off; as long as men exist the history of nature and the history of men are mutually conditioned.

Where speculation ends—in real life—there real, positive science begins: the representation of the practical activity, of the practical process of development of men. Empty talk about consciousness ceases, and real knowledge has to take its place.

As Karl Marx once noted: “Hegel remarks somewhere that all great, world-historical facts and personages occur, as it were, twice. He forgot to add: the first time as tragedy, the second as farce.” William Jennings Bryan and the Scopes trial was a tragedy. The creationists and intelligent design theorists are a farce.

Pavlov’s data on the two fundamental antagonistic nervous processes—stimulation and inhibition—and his profound generalizations regarding them, in particular, that these processes are parts of a united whole, that they are in a state of constant conflict and constant transition of the one to the other, and his views on the dominant role they play in the formation of the higher nervous activity—all those belong to the most established natural—scientific validation of the Marxist dialectal method. They are in complete accord with the Leninist concepts on the role of the struggle between opposites in the evolution, the motion of matter.

I’m one of those people that think Thomas Edison and the light bulb changed the world more than Karl Marx ever did.

Marx founded a new science: the science of history. … The sciences we are familiar with have been installed in a number of great “continents”. Before Marx, two such continents had been opened up to scientific knowledge: the continent of Mathematics and the continent of Physics. The first by the Greeks (Thales), the second by Galileo. Marx opened up a third continent to scientific knowledge: the continent of History.