In counterpoint to these attempts to reconstitute a unified epistemological field, we find at regular intervals the affirmation of an impossibility: this was thought to be due either to the irreducible specificity of life (which there is an attempt to isolate especially in the early nineteenth century) or to the particular character of the human sciences, which were supposedly resistant to all methodological reduction (the attempt to define and measure this resistance occurred mostly in the second half of the nineteenth century).