constructed that the questions which are posable within it already presuppose certain kinds of answer. Its fundamental structure is thus closed, circular and self-confirming: wherever one moves within it, one will always be ultimately returned to what is securely known, of which what is unknown is merely an extension or a repetition. Ideologies can never be taken by surprise, since like a counsel leading a witness in a law court they signal what would count as an acceptable answer in the very form of their questions. A scientific problematic, by contrast, is characterized by its open-endedness: it can be 'revolutionized' as new scientific objects emerge and a new horizon of questions opens up. Science is an authentically exploratory pursuit, whereas ideologies give the appearance of moving forward while marching stubbornly on the spot.

In a controversial move within Western Marxism, ⁴⁴ Althusser insists on a rigorous distinction between 'science' (meaning, among other things, Marxist theory) and 'ideology'. The former is not just to be grasped in historicist style as the 'expression' of the latter; on the contrary, science or theory is a specific kind of labour with its own protocols and procedures, one demarcated from ideology by what Althusser calls an 'epistemological break'. Whereas historicist Marxism holds that theory is validated or invalidated by historical practice, Althusser holds that social theories, rather like mathematics, are verified by methods which are purely internal to them. Theoretical propositions are true or false regardless of who happens to hold them for what historical reasons, and regardless of the historical conditions which give birth to them.

[. . .]

There is a difference between holding that historical circumstances thoroughly condition our knowledge, and believing that the validity of our truth claims is simply reducible to our historical interests. The latter case is really that of Friedrich Nietzsche; and though Althusser's own case about knowledge and history is about as far from Nietzsche's as could be imagined, there is an ironic sense in which his major theses about ideology owe something to his influence. For Nietzsche, all human action is a kind of fiction: it presumes some coherent, autonomous human agent (which Nietzsche regards as an illusion); implies that the beliefs and assumptions by which we act are firmly grounded (which for Nietzsche is not the case); and assumes that the effects of our actions can be rationally calculated (in Nietzsche's eyes yet another sad delusion). Action for Nietzsche is an enormous, if necessary, oversimplification of the unfathomable complexity of the world, which thus cannot coexist with reflection. To act at all means to repress or suspend such reflectiveness, to suffer a certain self-induced

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