David Hume and Immanuel Kant were the most important philosophers of the eighteenth century. Both have many followers today. In ethics, they are usually seen as opposites. Hume was a skeptic who denied that there are moral truths; ethics is from feeling, not reason. Kant was a rationalist with a rigid system of moral truths; ethics is based on pure reason.Reason and Desires
But Hume's thinking evolved. His later work gave a more balanced account of how reason and feeling work together.
These summaries and problems deal with Hume's Treatise of Human Nature and Enquiry Concerning the Principles of Morals. These materials are copyrighted (c) 1998 by Harry J. Gensler but may be distributed freely.
Reason is the discovery of truth and falsehood. A desire or action can violate reason only by involving a factual error (as when we want an apple that we falsely believe to be sweet) or by choosing means insufficient to our end.Morality Isn't from Reason
No desire in itself is either reasonable or unreasonable. 'Tis not contrary to reason to prefer the destruction of the whole world to the scratching of my finger.
Reason's only purpose is to help us to satisfy our desires. Reason is, and ought only to be, the slave of the passions.
Hume gave two arguments to show that morality isn't from reason. The "practicality argument" claims that judgments of reason by themselves have no influence on our feelings and actions. But moral judgments have such influence. So moral judgments aren't judgments of reason.Morality Is from Feeling
The second argument rests on Hume's Fork -- the claim that all truths are either relations of ideas or matters of fact. But moral judgments aren't "relations of ideas"; this means that they aren't conceptual truths, like mathematical ones, that are based on definitions and logical connections. Nor are moral judgments "matters of fact"; this means that they aren't empirical truths, like scientific ones, that are based on sense experience. It follows that moral judgments don't express truths -- and hence aren't from reason.
Only feeling can distinguish between virtue and vice; reason can't do this. Morality is from feeling, not from reason. Morality is more properly felt than judged.Nature
Virtue is distinguished by the pleasurable feeling that we get from considering the object, and vice by the painful feeling.
Why do we feel positively toward some things, and negatively toward others? Some such feelings are innate, as when we feel negatively about hunger. Others come from social conditioning, as when we feel negatively about stealing.
Morality isn't based on what is natural.Later Refinements
"Natural" has various senses. For example, what is "natural" may refer what is "typical" -- as opposed to what is "unusual." Or "natural" may be opposed to "artificial" or "miraculous."
In none of these senses is the natural always better than its opposite. The typical isn't always better than the unusual (since selfishness is typical and heroism unusual). Nor is the natural always better than the artificial. Nor is the natural always better than the miraculous.
So we can't equate virtue with the natural, or vice with the unnatural.
Hume's later writings give a larger role to reason in ethics. We use reason to understand the facts of the case; we can't make an adequate judgment if we are ignorant or misinformed. Once we understand the facts, we see how we feel from an impartial standpoint. So ethics needs both reason and feeling.
Impartiality distinguishes moral feelings from other positive or negative feelings. "X is evil" (unlike "X is my enemy") expresses feelings that abstract from our self-interest and take a general perspective based on love of humanity.
Hume defined "X is virtuous" as "X is a quality of mind that everyone who considers would find agreeable." Perhaps implicit is "... if the person fully understood X and were impartial." If so, then Hume held the ideal observer theory.