Descartes thought that belief was a voluntary matter. His account of error in the Fourth Meditation is based on this. Given his account of what it is to have a true idea he thought that our false beliefs could be accounted for by the fact that while our intellectual capacity is limited our capacity for willing is unlimited, and so allows us to give our assent to what we do not truly perceive. Spinoza, on the other hand, thought that the intellect and will cannot be separated in such a way, and urged that ‘In the mind there is no volition or affirmation and negation excepting that which the idea, in so far as it is an idea, involves’ (Ethics, Pt. 2, Prop. 49). One philosopher, S. Hampshire, sees this distinction between Descartes and Spinoza as one of the dividing lines of philosophy (Thought and Action, p. 155). Yet it is not easy to see wherein the division lies.