David Hume believed that empiricism had not been fully and consistently applied. He argued that there are only analytic and synthetic propositions, and that synthetic propositions must be derived from sense data. However, concepts like God and causality cannot be traced to sense data, making them "nonsense" according to Hume. Hume also argued that the self is an illusion, as when we introspect we only find particular perceptions and not a continuous self. Immanuel Kant sought to address problems with both rationalism and empiricism by arguing that while knowledge comes from sense data, the mind structures and organizes this data using innate categories like unity and plurality.

1. Empiricist Epistemology – Hume & Kant Unit 4