Highly original and challenging in its views, An Enquiry Concerning Human Understanding proved controversial upon its 1748 publication, and it remains so today. In terms of influence, David Hume's theory of causality ranks as the modern equivalent of Aristotle's work on the subject. Hume's philosophy roused Immanuel Kant from his self-described "dogmatic slumber," and inspired the thinking behind the Critique of Pure Reason, which introduced a completely new school of philosophy in the form of Kantian ethics. One of the most widely read works in philosophy and the best introduction to Hume's other works, An Enquiry Concerning Human Understanding asserts that causal relationships constitute the core of our understanding of relationships between objects in the external world. Hume establishes the factors that define a causal relationship between two objects and demonstrates that causal theory derives from the mind rather than experience. In so doing, he questions the basis of scientific causal theory, which claims validity by nature of its basis in experiential knowledge. Hume's assessment of the limitations of human understanding and the merits of skepticism make his Enquiry a work of enduring relevance and influence.