Hume's philosophy of morals has a number of important characteristics which it may be helpful to bear in mind before one reads the Enquiry itself. One of these is the sharp distinction which is made between the fields of logic and ethics. Logic has to do with man's activities as a thinking being; ethics and morality are concerned with his actions as a social being. Logic is a matter of reasoning, and its function is to ascertain facts; morals has to do with the field of values and cannot be derived from a mere statement of facts. It is true that reasoning is involved in both logic and ethics, but while logic is derived from the nature of reason, ethics is not.
No amount of factual data, however complete it may be, is sufficient to tell one what it is that he ought to do. You cannot derive what ought to be from what is. It is only because humans are feeling creatures as well as thinking ones that value distinctions are possible and can indicate what it is that one ought to do. Failure to recognize these distinctions between the fields of facts and of values has in Hume's judgment been responsible for much of the confusion and the misunderstanding which has been characteristic of moral philosophy. By showing that moral judgments have their origin in the feelings rather than the intellect, he hopes to correct this situation. The procedure for determining facts is not the same as it is for recognizing distinctions of value.
Hume's position is in this respect similar to that of Immanuel Kant, who recognized the difference between what he called the pure, or theoretical, reason and the practical reason. The theoretical reason belongs to the understanding, and its function is to enable one to arrive at a true or correct knowledge of the facts. Practical reason is that particular function of the mind that enables one to know what it is that he ought to do. Theoretical reason is the work of the intellect, but practical reason pertains to the will, or that which moves people to act. It is true there are many points of contrast in the moral philosophies of Kant and Hume, for Kant was a rationalist in his conception of morals and Hume was not. However, they were in agreement insofar as they both recognized an important difference between judgments of fact and judgments of value.
