The work of Immanuel Kant is immense and incredibly complex. However, the common theme throughout all of his work is his use of a critical method to understand and come to terms with philosophical problems. Kant believed that in philosophy, one should not speculate about the world around him; rather, we should all critique our own mental abilities. We should investigate all that we are familiar with, understand and define the limits of our knowledge, and determine how our mental processes affect how we make sense of everything. Rather than speculating on the universe around us, Kant believed that by looking inward we would discover the answers to the many questions posed by philosophy. Thus, Kant shifts away from metaphysics and toward epistemology (the study of knowledge).
To understand Kant’s philosophy of transcendental idealism, one must first understand Kant’s distinction between phenomena and noumena.
Kant claims that we only have the ability to know the world that is presented to us from our minds and that the external world can never truly be known. In other words, the only knowledge that we know, and ever will know, is knowledge of phenomena. This means that knowledge of noumena is, and always will be, unknown.
In philosophy, idealism refers to the various notions that share the belief that the world is composed not of physical things, but of mental ideas. In Kant’s transcendental idealism, however, Kant does not deny that an external reality exists. Nor does he assume that things are less fundamental than ideas. Instead, Kant claims that our minds contextualize and limit reality, and that we will never be able to transcend these limitations.
The Synthetic A Priori
Kant attempts to answer the question of how, when the nature of experience is individual and particular (for example, we each experience sights and sounds individually), there can be universal truths from experience. How can we infer cause and effect when we cannot experience (see, smell, touch, etc.) the law of causation?
Kant makes a distinction between two types of propositions:
- Analytic proposition: This is when the concept is contained within the subject. For example, “all squares have four corners.” In this sentence, four corners is part of the definition of a square.
- Synthetic proposition: This is when the concept is not contained within the subject. For example, “all women are happy.” In this sentence, happiness is not part of the definition of a woman.
Kant then makes a distinction between two more propositions:
- a priori proposition: This is when the justification of a proposition does not rely on any experience. For example, “8 + 6 = 14” or “all mice are rodents.”
- a posteriori proposition: This is when the justification of a proposition relies on experience. For example, the proposition “all women are happy” requires experience to say whether or not it is true.
Kant asks how synthetic a priori knowledge can be possible (in other words, how one can know something is universal and necessary without it being definitional or self-evident). Kant concludes that synthetic a priori knowledge is in fact possible. And here’s how:
According to Kant, experience is organized in our mind based on certain categories. These categories then become features of experience that are both necessary and universal. For example, it is not that we can’t find causation in nature. Rather, causation is a feature in our minds, so we always perceive it. We can’t not find causation. The synthetic a priori, according to Kant, is how people develop substantive knowledge.