3.5: David Hume

Of the philosophers discussed here, David Hume (1711-1776) has probably had the greatest influence on contemporary analytic philosophy. The twentieth century begins with a movement known as Logical Positivism that tests the limits of Empiricism. The Empiricism of the Logical Positivists is heavily indebted to Hume. Hume’s empiricist epistemology is grounded in his philosophy of mind. Hume starts by asking what we have in the mind and where these things come from. He divides our mental representations into two categories, the relatively vivid impressions, these include sensations and feelings, and the less vivid ideas which include memories and ideas produced by the imagination.

What distinguishes impressions from ideas in our experience is just their vividness. The picture of the mind Hume offers is one where all of our beliefs and representations are cooked up out of basic ingredients provided by experience. Our experience gives us only impressions through sense experience and internal impressions like feelings. From this we generate less vivid ideas. Memories are merely faint copies of impressions. Through the imagination we can generate further ideas by recombining elements of ideas we already have. So through impressions we get the idea of a lizard and the idea of a bird. We can then generate the idea of a dragon by imaginatively combining elements of each. In cooking up new ideas from old ideas, the imagination is guided by associating relations like resemblance, contiguity (next-to-ness) and cause and effect. So, for example, an impression of a grapefruit might lead me to think of an orange due to their similarity. The thought of my bicycle might lead me to think of the table saw it is parked next to in the basement. Through the association of cause and effect, my idea of a struck match leads me to the idea of a flame. The last of these principles of association, cause and effect, turns out to be faulty for reasons we will examine shortly.

The imagination is not merely a source of fancy and fiction. The imagination also includes our ability to understand things when we reason well in formulating new ideas from old ones. A priori reasoning, which is reasoning independent of experience, can produce understanding of relations of ideas. Mathematical and logical reasoning is like this. When I recognize the validity of an argument or the logic behind a mathematical proof, the understanding I attain is just a matter of grasping relations between ideas. But a priori reasoning only reveals logical relations between ideas. It tells us nothing about matters of fact. Our ability to understand matters of fact, say truths about the external world, depends entirely on a posteriori reasoning, or reasoning based on experience. As we will see, our ability to reason about matters of fact doesn’t get us very far.

Often our philosophical confusion is the result of having added more than we are entitled to add to our experience when we are striving to understand it. Hume aims to correct many of these errors and, in doing so, he aims to delineate the limits of human knowledge and understanding. As it turns out, we don’t know as much as we commonly suppose, in Hume’s opinion. The result of Hume’s rigorous Empiricism is skepticism about a great many things. Some of Hume’s skeptical results are not so surprising given his Empiricism. Hume is skeptical about objective moral truths, for instance. We don’t get to observe rightness and wrongness in the way we can see colors and shapes, for instance. The idea that there are objective moral truths, according to Hume, is a mistaken projection of our subjective moral sentiments.

Hume is not worried that his subjectivism about morality will lead to moral anarchy. Note that the opinion that it’s OK to do whatever you want is itself a moral opinion. So, for the subjectivist, “anything goes” is no more rationally justified than any other moral opinion. While Hume does think that morality is concerned with subjective sentiments, not objective facts, the lack of objective moral truths won’t corrupt us or undermine the social order because we all have pretty much the same sorts of moral sentiments and we can base a sensible social order on these. While we may feel differently about specific practices or principles, Hume thinks we have a basis for negotiating our moral differences in our more general and more or less universally shared moral sentiments of self-love, love for others, and concern for happiness.

Hume’s skepticism about objective moral truths now strikes many people as common sense. But the empiricist epistemology that leads him to subjectivism about morality also leads him to skepticism about causation, the external world, inductive reasoning, about God, and even about the self. We’ll examine these further skeptical conclusions starting with causation.