One of the main reasons why Hume insisted that moral judgments are based on feelings rather than the intellect is that a mere awareness of facts is powerless to move one to act. People act as a result of their feelings and desires, and while it is true that these may be influenced by what they believe to be the facts, it is not the knowledge alone that moves the will or restrains it from acting. In the Treatise of Human Nature, Hume had said, "Tis not unreasonable for me to prefer the destruction of the whole world to the scratching of my finger." The purpose of this statement was to emphasize the fact that preferences, like all moral obligations, arise from the feelings and cannot be derived from a mere awareness of the facts.
Throughout all of his writings, Hume made use of the empirical method in his philosophy. Following the trend which had been established by such thinkers as Francis Bacon, John Locke, and George Berkeley, he held that all it is possible for anyone to know about themselves or the world in which they live must be derived from the facts of experience. There is no way of determining the nature of that which goes beyond the world of experience, and the belief in the possibility of such knowledge has been one of the main sources of dogmatism and the various forms of intolerance that have usually been associated with it.
In his analysis of the human understanding, Hume had applied the empirical method in order to find an explanation for the way in which ideas are formed. Like other empiricists who had preceded him, he assumed that all ideas are derived from sense impressions, but on the basis of this assumption he went beyond the work of his predecessors and denied the possibility of any genuine knowledge of anything that transcends the data which is supplied by the senses. This means that no one can have any knowledge of an external world, of a material substance, a spiritual substance, a self, or of God. While it was clear enough that one may believe in the reality of any or all of these objects, it was pointed out that there is no logical foundation for these beliefs nor for the existence of the objects to which they refer.
