 The content of the laws of progress, however, is an object of contention. Many thinkers, including Hegel and Auguste Comte, view the development of ideas over time as the fundamental change that causes overall improvement.  Marx, in contrast, regards the growth of the means of production as primary.  Kant represents a third category, arguing that a tension within human nature itself is the source of change.  We will also see theorists who offer more eclectic causal stories and, because their accounts of change are more complicated, are less inclined to formalize their conclusions.  Next to content, thinkers differ in their treatment of episodes of devastation and conflict and periods of decline.  It is hard for anyone to sustain the argument that improvement is perfectly linear, but some theorists more than others emphasize that such episodes and eras can be part of a pattern of long-term improvement.  Furthermore, the extent to which the laws are deterministic varies.  Some authors leave little room for choice and contingency, while others frame their generalizations as loose trends that constrain rather than determine the course of events.  Authors in the latter category often present their writings as political interventions that can shape the future as well as predict it. 