From Descartes to Kant in Two Pages
In almost thirty years of college teaching, I wrote many things for my students, most of which is long since lost. I have been perusing the surviving material and have found some that might be of interest. Here is one such piece. This particular file originally came with this disclaimer: “This overview was written hastily this morning without consulting the book. If any of it conflicts with the book’s explanation, favor that explanation. ” I still issue the disclaimer.
Descartes wants to know what’s true. He begins by doubting everything and argues that knowledge derives from the certainty of the existence of one’s own consciousness and the innate ideas it holds. Primary among these innate ideas are mathematical ideas and the idea of a God. Upon this foundation he claims all knowledge is built.
Locke argues that innate ideas are just another name for one’s pet ideas. Instead, he argues, knowledge is based on the experience of sense data. Locke realizes that we only know things as we experience them, we don’t know the essence of the substances that make up the world. Retreating from the skepticism this implies, he accepts the common sense view that our perceptions correspond to external substances in the world.
Berkeley realizes that we can have perceptions without there being an external world at all. In fact things exist only to the extent they are perceived, and thus non-perceived things don’t exist. Recognizing the implications of this radical philosophy—which until this day no one has refuted—Berkley claims there is a God who is constantly perceiving the world and thus in the end the world is real.
Hume follows this thinking to its logical conclusion. We have perceptions, but their source is unknown. That source could be a God or Gods, some other powerful beings, substances, the imagination, etc. At the same time he applies this skepticism about the existence of the external world to morality, science and religion. Scientific knowledge is not absolute because there are problems with the idea of cause and effect as well as with induction. Still, Hume does believe that mathematics and the natural sciences are sources of knowledge.
Hume’s attack on religion is one of the most famous in the history of philosophy, and he ranks with Feuerbach, Marx, Neitzsche, and Russell as one of religion’ great critics. His article against the possibility of miracles is the most celebrated piece on that subject ever written. He says there is never any reason to believe in miracles, defined as a suspension of natural law.
For example, take the case of virgin births or resurrections from the dead. Such stories are found in many religions and throughout pagan mythology. But in all these cases Hume asks whether it is more likely that such things actually happened, or that these are myths, stories, lies, deceptions, etc. Hume argues that its always more likely that reporters of miracles are deceiving you or were themselves deceived, than that the supposed miracle actually happened. In short, Hume is a skeptic; he doesn’t believe without evidence.
Perhaps most importantly, his philosophy sets the stage for the coming of the man who is considered the greatest of modern philosophers, a man who said that Hume had “awakened him from his dogmatic slumber,” a man who wants to respond to Hume’s skepticism and show that mathematics, science, ethics, and the Christian religion are all true.
Immanuel Kant was one of the first philosophers who was a professor. He was a pious Lutheran, and a solitary man who never married. He was the author of some of the most esoteric works in philosophy, who devoted nearly every waking hour of his life to philosophy. Troubled by Hume’s skepticism, Kant looked again at both rationalists like Descartes and empiricists like Locke, Berkeley, and Hume. Kant believed that the problem with rationalism was that it ultimately established great systems of logical relationships ungrounded in observations. The problem with empiricism was that it lead to the conclusion that all certain knowledge is confined to ideas.
Kant thought that if we accept the scientific worldview, then belief in free will, soul, God, and immortality were impossible. Thus Kant’s project was to reconcile rationalism and empiricism, while at the same time showing that God, free will, knowledge, and ethics are possible. (In some ways all of philosophy since Descartes has attempted to show how the scientific worldview can be reconciled with many people’s notions of free will, meaning, God, and morality.)
Kant’s Epistemology – Kant argues that rationalism is partly correct—the mind starts with certain innate structures. These structures impose themselves on the perceptions that come to the mind. In other words, the mind structures impressions, and thus knowledge results from the interaction of mind and the external world. (Kant describes many of these mental structures, which he calls categories of the understanding and forms of sensibility. These forms and categories—like cause and effect, time, and space—shape what the senses receive, thus making some sense of perceptions.) Thus both the mind and sense data matter in establishing truth, as the success of the scientific method had shown.
Kant’s Copernican revolution placed the mind, rather than the external world, at the center of knowledge. What we can know depends upon the validity of what’s known by the structures of the mind. But is metaphysical knowledge justified? Can we know about the ultimate nature of things, things beyond our experience? For example, can we know if there are there Gods, souls, ghosts, free will, and immortality?
To answer this question Kant asks what pure reason knows, that is, reason without the addition of sense experience. What he realizes is that all we can know are phenomena, that is experience or sense data mediated by the mind. Since all our minds are structured similarly, we all have the same basic sense experiences. But we cannot know “things-in-themselves,” that is, things as they actually are. Thus there is a gap between human reality—things as known to the mind—and pure reality, things as they really are.
To bridge this gap Kant proposes regulative ideas—self, cosmos, and God—which serve to make sense of our experiences. We must presuppose a self that experiences, a cosmos to be experienced, and a cause of the cosmos which is God. Kant grants that we can’t know if any of things exist, but that is it a practical necessity to act as if they do. We cannot have experiences without there being a knower, a known, and God. Since we do have experiences, Kant concludes that these regulative ideas probably correspond to real existing things.
