Some scholars characterize Schelling as a protean thinker who, although brilliant, jumped from one subject to another and lacked the synthesizing power needed to arrive at a complete philosophical system. Others challenge the notion that Schelling's thought is marked by profound breaks, instead arguing that his philosophy always focused on a few common themes, especially human freedom, the absolute, and the relationship between spirit and nature. Unlike Hegel, Schelling did not believe that the absolute could be known in its true character through rational inquiry alone.