There is a relatively large literature in feminist sociology which starts from Marx. Hamilton (1978), for example, used Marx as the fundamental theorist for understanding how women experienced the passage from feudalism to capitalism in Europe. Feminist writers in Third Wave feminism were critical of Marx’s failure to address sex differences among workers, explore exploitation inside the family, make the labour of reproduction as significant as that of production, and theorise sexuality. Marx’s own life, especially his treatment of women in his family and household, also causes problems for feminists. However, key concepts, such as ideology and false consciousness with Marxist origins are widely used in feminism. The empirical studies of women in employment (e. g. Cavendish, 1982; Cockburn, 1983) used Marxist ideas to address issues that both Marx himself and contemporary feminists could recognise. From 1968 until the fall of the Berlin Wall in 1989 many Marxist feminists worked with a dual system approach, in which Marxist theories were used to analyses the means of production, but other sources were used to theorise sexuality. Michele Barrett (1988) is a leading exponent of such an approach. Heidi Hartmann (1979, 1981) wrestled with what she called ‘the unhappy marriage’ of feminism and Marxism. Several feminist sociologists researched and challenged the ways in which Marxist ideas had been implemented in state socialist countries such as the USSR, and Czechoslovakia (e. g. Heitlinger, 1979; Scott, 1974), in the process critiquing Marx himself.