Widely considered a classic of modern philosophical literature, An Enquiry Concerning Human Understanding is David Hume's delineation of his theory of knowledge, a work that would influence thinkers both in his time and for generations to come. Proceeding in incremental steps, Hume discusses the following concepts: The Different Species of Philosophy, The Origin of Ideas, The Association of Ideas, Skeptical Doubts Concerning the Operations of the Understanding, Skeptical Solution of These Doubts, Probability, The Idea of Necessary Connection, Liberty and Necessity, The Reason of Animals, Miracles, "Of a Particular Providence and of a Future State," and "The Academical or Skeptical Philosophy.".