Marx’s idea is that economic structures rise and fall as they further or impede human productive power. For a time— perhaps a very long time—an economic structure will aid the development of productive power, stimulating technological advances. Yet, Marx believes, this will typically last only so long. Eventually any economic structure (except, apparently, communism) starts to impede further growth. In Marx’s terminology, it ‘fetters’ further development of productive power. Technology just cannot grow within the existing economic structure. At this point the economic structure is said to ‘contradict’ the productive forces. But this contradiction cannot continue indefinitely. There will come a time when the economic structure cannot hold out any longer, for it cannot hold up progress—the development of the productive forces—for ever. The ruling class will begin to lose its grip, and, at this point, Marx says, the economic structure will be ‘burst asunder’ leading to a period of social revolution. Just as one form of society is replaced by another, one ruling class falls away and another becomes dominant. This is how capitalism is said to have replaced feudalism, and will be how capitalism falls to communism.