Cause and Effect: Humean Doubts and Kantian Answers

          To understand David Hume's criticism of the idea that we can know, in a robust and philosophical way, that there is a connection between what we call causes and effects, we must first examine how he thought our minds related to the world. Unlike the Rationalists that came before him, Hume was skeptical that reason and intuition were all that we needed for knowledge. For Hume, the first contact that we have with any object (if it exists at all) is the appearance the object has on our senses, so that the first thing that we are aware of is an impression that we have.¹ Humean impressions are not simply limited to our sensual perceptions of the potential objects around us, but are also of every possible thing that we might experience, including our own internal mental processes, like emotion-states and first-order desires. Impressions are not just what we see, feel, taste, etc., but how we feel, what we want, and what motivates us. In short, impressions are the way that we first experience everything.

          From those impressions, content is directly added into the mind and forms ideas that share the same content. Hume thought this was a matter of common sense, anyone could see that while reflecting upon the painful experience of touching a burning hot object, we almost feel the same pain, but with less force than if we were actually touching something hot.² To Hume, the impression had a strength to it that could never be matched by a mere idea, but impressions only differed from ideas in strength; the content was copied directly into the idea exactly as it was in the impression.³

          Once a series of impressions has formed a series of ideas, the imagination tends to form perceived connections between the ideas, and those connections can be evaluated according to any number of relationships they bear to each other.⁴ The comparative work is not a function of perception, but of imagination, and as such, it cannot involve working with impressions, but only with ideas. Of all possible relations, Hume thought that they fell into seven broad groups: resemblance, identity, space and time, quantity, quality, contrariety, and cause and effect.⁵ From the comparison of ideas, the imagination then sorts the ideas in a way that allows us to make sense of the impressions we receive.