What is Transcendental Idealism?
Transcendental idealism can be understood on two ways. On a topical level it can represent the whole of Kant’s enlightenment philosophy, and in the context of his epistemology, transcendental idealism is to be distinguished from rationalism & empiricism. Kant’s philosophy is often thought of as a blend of rationalism & empiricism and transcendental idealism became a way to identify Kant’s particular contribution. However, this way of defining transcendental idealism does not actually define what the term means in Kant’s overall project (it merely describes his philosophical position as a blend of empiricism & rationalism).
The easiest route is to divide the term in half, first looking at the term: transcendental. This can be understood as a ‘going beyond’ the matter at hand. To transcend something means to ‘go beyond’ what that something actually is in experience. The classic example: ‘all bachelors are unmarried’ is one such example of this ‘going beyond’. In other words, we ‘go beyond’ experience with the epistemological claim that bachelors are unmarried—we have no need to go out into the world to have certainty that bachelors are unmarried. Such knowledge is known “beyond” experience. Now also acknowledge that what we are describing here is also the way a priori thinking is understood.
With Kant, whatever is transcendental, at the same time describes the particular way in which we think using our a priori reasoning. When we conclude with certainty that a bachelor is unmarried our thought, our cognition, our knowledge is transcendental—we ‘go beyond’ experience in order to affirm this type of a priori knowledge about the world.
Idealism, the other half of the term, is the philosophical (epistemological) position whereby the content of the way in which the world appears to us is mind-dependent. Kant’s epistemology is often characterized by the notion that the world as it is known to us is dependent on the very reasoning we use to understand it. That the world of experience, for example, has a certain causal order is not something we simply observe, but it is the way in which the world is understood by us in a rationally ordered way. Our rational mind constructs the way the world is experienced. A sequence of causal events is not just an observation it is also a construct of our a priori knowledge. This is idealistic because the way in which the world appears to me is mind dependent.
So idealism is different from realism in the sense that realism claims that if a tree falls in the forest & we’re not around to hear it, it still makes a noise. With Kant’s idealism a tree falling out of ear-shot would describe something that falls outside of the way the world appears to us, therefore it might be what Kant named the “thing-in-itself”, that part of things we’ll never have a grasp of.
How does Kant’s transcendental idealism move from Hume’s empiricism?
Hume’s critique of causality awoke Kant from his ‘dogmatic slumbers’ because Hume was astute enough to observe that there is no necessity to be found in any causal connection. Hume is an empiricist who based all the way we know of the world is through sense experience alone. When Hume called into question the very notion of necessity as absent from causation, his empirical skepticism pointed to something we typically identify as reason itself. Kant seizes this opportunity to make a claim for the necessary connection Hume is finding absent in experience. Why?—because it is reason that supplies the connection according to Kant. Hume was on to something & Kant resolves it with a priori reasoning. This is the missing part of Hume’s critique that Kant grabs onto as obviously product of reason itself. In other words, a causal relationship is one that is considered to be a ‘category of understanding,’ for Kant, which is a fancy way of saying it involves reasoning alone to understand a cause & effect relationship at its necessary core. The necessary connection is not found in experience as Hume empirically observed. Kant agrees with this & shows that the necessary connection is not a matter of habit as Hume posited, rather it is an act of reason that supplies the necessary connection we find when one an effect causes something to happen.
Even if we understand causation rationally, we need the experience of it in order to know what to do with it. Kant shows us that we cannot have one without the other. Say for example, I already know that reason supplies the necessary connection between an effect & cause. That’s a pretty minimal way in which to understand the world, given that cause & effect relationships are everywhere. We need to think of the particular empirical manifestation of casual relationships so as to know how to understand their specific relationships & significance.