Kant asserted in the book “Prolegomena to Any Future Metaphysics” that the point of departure for Hume was mainly from a single but vital concept in metaphysics known as the connection of causes and effects. He went further to claim the originality of generalizing Hume’s doubts about causation to other metaphysical concepts so as to answer these doubts about causation as part of a more general defense of knowledge. Kant’s defense of the concepts of both object and causation are basically a section of a single larger argument concerning the conditions of the possibility of a form of knowledge that Hume seem to have ignored.
Kant’s greatest question is how synthetic knowledge a priori is possible. By this, Kant asks how we can acquire knowledge about the world without inferring this knowledge from experience. Kant’s claim is that we can gain knowledge of the facts about the empirical world a priori. Kant sees the defense of synthetic a priori knowledge as vital to defeat skepticism. In order to understand how this is so, it is important to consider Hume who believed that all knowledge concerned either relations of ideas or matters of fact.
In some sense, this is Kant’s differentiation between analytic and synthetic truths. According to Hume, knowledge of the relations of ideas could be achieved by intuition and demonstration. In Kant’s terminology, it could be attained a priori. Kant and Hume agree up to this point. However, Hume goes further to claim that all knowledge of matters of fact comes from experience. Put in another way, he claims that all synthetic knowledge is a posteriori. The question is, how do we arrive at knowledge on the basis of experience?
First, we can arrive at this knowledge by observation. We can know of the existence of something by observation. However, there are a limited number of our beliefs concerning the world that we have actually observed directly. A large proportion of what we think of as our knowledge needs experimental inference which is also Hume’s second main method of knowledge acquisition. From observations, we infer the cause or what explains them. For instance, from observing footprints, one may conclude that someone had walked in that particular direction.
However, arriving at such a conclusion requires that we need more than just the observation of the footprints. Knowledge of the causal laws relevant to the production of footprints is also necessary. Up to this point, the conclusion is that a large percentage of synthetic knowledge is derived from experimental inference which also requires knowledge of causal laws. Synthetic knowledge therefore requires a prior knowledge of causal laws. The possible sources of this knowledge are the subject of Hume’s investigation.
Hume maintains that the experience which results in the belief that one set of events causes another set of events is the experience of constant conjunction. In other words, if we observe that stepping on sand is regularly followed by production of footprints, then we may arrive at a conclusion that stepping on sand causes footprints. However, this statement that stepping on sand causes footprints implies that the first is always followed by the second and this again implies a prediction about the future; that is, steeping on sand produces footprints.
The question that remains is how we can know that this prediction is true. Generally, we know that something is true if we see that it is so or we know that something is true if we infer that it is true from our observation or by either deduction or experimental inference. No one can however see into the future. This leaves us with deduction and experimental inference. Deduction can be ruled out since there no contradiction is involved in the supposition that the future will not look like the past. It does not appear to be analytic, a matter concerning the relation of ideas, that the future will resemble the past.
The only option left is experimental inference which according to Hume is dependent on knowledge of cause and effect. A circle is now completed; what we are seeking is a justification of our knowledge of cause and effect, the answer to which we have found to be dependent upon the knowledge of cause and effect, which offers no help at all. It appears like a general skeptical conclusion has been arrived at worse. A large percentage of our knowledge is dependent upon experimental inference; experimental inference depends on knowledge of cause and effect; however, there is no way of acquiring such knowledge.
It appears as if experimental inference does not offer knowledge at all, and therefore, very little is known about the world. Kant agrees with Hume that a large percentage of our knowledge lies on knowledge of causality and further agrees that we cannot acquire knowledge such as the law of causality a posteriori. However, Kant endeavors to prove that we can have knowledge of causality a priori. Due to the fact that knowledge of causality is vital for the majority of the rest of our knowledge, Kant’s defense of our synthetic a priori knowledge also acts as a defense for the majority of ordinary a posteriori knowledge.
Kant’s epistemological motivation emanates from the desire to defend knowledge about the natural world from the skeptical challenge of Hume. According to Kant, we can acquire knowledge about the empirical world without founding this knowledge on experience. With regard to how this kind of knowledge can be acquired, Kant holds that the empirical world has been made by us according to certain rules and we can therefore know a priori those characteristics of the world that we have put there in the first place.
This is an interesting position as Kant seems to place humans at the center of the universe. Kant conceives of the general features of the observable world to exist not because they are things in themselves but because we place them there (Kant). As such, the explanation for time, space, causality and other features of the universe is not to be derived from the world itself but in our own mental composition. Kant’s epistemology is designed to counter skepticism even though his view contains a number of claims that appear skeptical.
For instance, he holds that it would be absurd to hope that we can know more of any object without experience of it or lay claim to the most minute of knowledge about anything assumed to be an object of possible experience which will determine it according to the constitution it possess in itself (Kant). Even though he argues against Humean skepticism and Berkeleian idealism, his position often appears to be an odd integration of the two. Kant insists that all our knowledge is knowledge of what he refers to as appearances.
Appearance is in most cases contrasted with reality and thus, this position seems to be a denial that we can know anything about reality. This apparent link may somehow be misleading since Kant views the entire empirical world as a collection of appearances. Kant for a moment is not skeptical that we know quite a number of things about objects that are external to ourselves. He believes that natural science and mathematics provide such knowledge. According to Kant, the conventional distinction between reality and appearance is a distinction within the realm appearances.
For Kant, there is something subjective about appearances and therefore about the entire empirical world. We partly create the world of appearance even though Kant thinks that there is a really real world that stands behind this appearance that we have nothing to do with. This real world is independent of our knowledge. The empirical world is objective in the sense that it is the same to everyone. In other words, it is intersubjective. However, it is subjective in the sense that it is a uniquely human world.
Kant seem to integrate Hume’s approach with Berkeley’s when he insists that empirical reality is a function of appearance while on the other hand holding that we can know nothing of the real world. This negative aspect of his doctrine, as much as it does not interfere with any of our practices, appears to be as skeptical as a die hard skeptic could wish. It is very important that three related doctrines of Kant are distinguished. The first one is that we cannot possess knowledge of anything we cannot experience. Put in another way, anything that transcends experience is unknowable.
The second doctrine is that we can possess no experience of things in themselves. From the first and the second doctrine, it follows that we cannot know anything about things in themselves, even though majority of people who accept the first doctrine would want to reject the second. His third doctrine is that freedom, immortality and God are classified under things in themselves, and therefore under things about which we cannot know anything. This third doctrine is entirely unjustified in my view. The knowledge of these matters is as direct as the knowledge of theoretical parts of physics or the more primitive parts of history.
If there exists a distinction between the phenomenal and the noumenal, then God and other related aspects belong to the phenomenal even though if at all they exist, then they possess noumenal underpinnings like anything else. Given that Kant’s insistence on the unknowability of things in themselves has to do with protecting God from the failure of argument concerning his existence, and from protecting freedom from the law of causality, accepting my view means that he will have minimum reason for insisting on the sharp difference between knowable phenomena and unknowable noumena.
With this regard, Kant’s motivation is to thwart skepticism and as much as his philosophy is anti-skeptical, it also appears to be very skeptical. Hume’s skepticism seemed unavoidable when looked at philosophically even though untenable psychologically. The process by which we arrive at a belief in an infinite independent world from mere appearances was characterized by error. If that is the way that belief emerges then it is unlikely to issue in knowledge.
The individual who doubts the external world trades on particular epistemic asymmetry between knowing one’s own states and knowing of external states. He accepts knowledge of the former and insists that this is the farthest we can go. The skeptical problem arises when one asks how he can proceed from the starting point to the conclusion that there is an external world. This is true for Hume as he begins with ideas and impressions. The question then remains how any sequence of these things lead to belief in enduring objects. Reference Kant, I. (1951). Prolegomena to Any Future Metaphysics. Forgotten Books