Spinoza was a thoroughgoing determinist who held that absolutely everything that happens occurs through the operation of necessity. For him, even human behaviour is fully determined, with freedom being our capacity to know that we are determined and to understand "why" we act as we do. By forming more "adequate" ideas about what we do and our emotions or affections, we become the adequate cause of our effects (internal or external), which entails an increase in activity (versus passivity). This process allows us to become both more free and more like God, as Spinoza argues in the Scholium to Prop. 49, Part II. However, Spinoza also held that everything must necessarily happen the way that it does. Therefore, humans have no free will, despite strongly believing that they do. This illusionary perception of freedom stems from human consciousness, experience, and indifference to prior natural causes. Humans think they are free, but they ″dream with their eyes open″. For Spinoza, our actions are guided entirely by natural impulses. In his letter to G. H. Schuller (Letter 58), he wrote: "men are conscious of their desire and unaware of the causes by which desires are determined."