Hume on Human nature. A Treatise of Human Naturepage 1 of 2 Summary, Book I: Of the Understanding Hume begins by arguing for the validity of empiricism, the premise that all of our knowledge is based on our experiences, and using this method to examine several philosophical concepts. First, he demonstrates that all of our complex ideas are formed out of simpler ideas, which were themselves formed on the basis of impressions we received through our senses. Therefore, ideas are not fundamentally different from experiences. Second, Hume defines matters of fact as matters that must be experienced, not reasoned out or arrived at instinctually. Based on these two claims, Hume attacks metaphysical systems used to prove the existence of God, the soul, divine creation, and other such ideas. Since we have no experience of any of these things and cannot receive a direct impression of them, we have no real reason to believe that they are true. Despite his apparent hostility to abstract ideas of a metaphysical nature, Hume does not deem all abstract ideas worthless. Hume argues that the mind naturally forms associations between ideas from impressions that are similar in space and time. In the mind, a general term becomes associated with further specific instances of those similar impressions and comes to stand for all of them. This process explains why we can visualize particular events that we may not have actually experienced, based on their association with those events that we have experienced. The theories Hume develops in the Treatise have their foundations in the writings of John Locke and George Berkeley, and Hume is associated with these two men as the third in the series of great British empiricists. Like Hume, Locke denied the existence of innate ideas, dividing the sources of our ideas into two categories: those derived from sensation through the use of our sense organs and those derived from reflection through our own mental processes. Hume makes use of Lockes distinction in his own theory of ideas, though he alters the terminology. For Hume, sensations and reflections both fall under the term impressions, while he reserves the term ideas for the results of mental processes such as imagination and memory. Humes discussion of abstract ideas rests on his acceptance of Berkeleys claim that the idea we have of a general term always springs from a specific experience, though used in a general way. Hume praised this explanation but further clarified how a general term could stand for several similar, but specific, experiences. Humes third philosophical tool is the fork, the principle that truths can be divided into two kinds. The first kind of truth deals with relations of ideas, such as true statements in mathematicsfor example, that the sum of the angles in a triangle equals 180 degrees. These kinds of truth are necessaryonce theyve been proven, they stay proven. The second kind of truth deals is in matters of fact, which concerns things that exist in the world.