Abstract: In Foucault's early research on madness history which contains four stages, the path of reason repressing non-reason gradually transformed the connotation of non-reason from being "arational" to "irrational" in a subtle manner. The former is not being rational, but is compatible with complete reason. The latter is not being rational either and resists reason in the narrow sense, namely rationality. This path was strengthened in his later study which focused on Kant's idea of enlightenment and thus led to the thought of eventalization. Theory has pushed this process forward. This thesis presents an extended explanation of this important issue, and reveals the fact that Post-Theory has inevitably gone to literature.

Key words: Foucault, critique of reason, arational, irrational, theory