The closer we get to Kierkegaard’s time, the closer we get to epistemologies that more closely reflect Kierkegaard’s understanding of religious and ethical knowledge. Kant, for example, provides a sort of middle way — or perhaps a better way to say this is that he provides a method that transcends the boundaries set out by the rational and empirical models of knowledge from Descartes to Hume. If we’ll remember, Descartes tended towards a heavy rationalism — doubting what he could not know with certainty until he could ascertain knowledge a priori that couldn’t be doubted. From this point, he attempted to build a system (internally) that couldn’t be doubted, and that gave him clear, reliable knowledge of the exterior world.
Hume (and his philosophical forebears) essentially thought this was rubbish. Knowledge is only accessible via sense experience. There are many reasons he thought this, but suffice it to say that the only knowledge he thought was even valid was knowledge that we gain “sensibly.” Through experience with the external world, we gain impressions (the immediate experience of the object with which we are interacting), and our minds create “ideas” from those impressions. Those ideas are our mind’s re-creation of those impressions, allowing us to observe them, post-experience. One of the main problems that Hume faced here is that he couldn’t prove causation via purely empirical evidence. But since he refused to acknowledge the existence of a priori knowledge, and we can’t prove that an effect was caused by something prior to a specific event occurring via sense experience, we’re stuck saying we can’t prove causation. The best we can do is say that, based on observation, we can reasonably expect that event B will follow event A because, historically, that’s what has happened before.
Kant sought a middle way here, and was, I think relatively successful. In fact, I think he was so successful that most of us still operate under Kantian or neo-Kantian epistemological assumptions. His solution? We do bring prior (a priori) forms to our experience of the world, but those forms are void of content. What are these a priori forms? Primarily space and time, but also things like causation. When we experience the world, we never experience it outside of these forms. Therefore, while those forms are not empirically extant, we bring along those forms with us. Copleston, in his History of Philosophy, Vol. VI, likens it to a man wearing rose-tinted glasses that he cannot remove. This man can still experience the world, but he can experience it in no other way than as rose-tinted. Space, time, and causation, according to Kant, are our rose-tinted glasses. Why is this useful knowledge? Because, if we know that we experience it as such, we can make other claims about reality that we couldn’t have made before, and it can perhaps explain our experience of phenomena (things that exist and/or occur) that do not otherwise make sense under empirical or rational models of epistemology.
Now, this is a serious distillation of Kant’s system, and his arguments that get us here are dense. But it seems as if we can at least recognize that this form of understanding how and why we know things informs how we understand epistemology today. Later, I’ll talk about his discussion of the limits of human reason, and how his epistemological system determines what we can know in the ethico-religious sphere.