In full, Prolegomena to Any Future Metaphysics That Will Be Able to Come Forth as Science (De. Prolegomena zu einer jeder künftigen Metaphysik, die als Wissenschaft wird auftreten können). Published 1783.

This relatively short work is an explication of Immanuel Kant's much larger Critique of Pure Reason (q.v.). In it, Kant explains the principle aims and results of the Critique, as well as his methodology. The Prolegomena, intended to arouse interest in and defend against criticism the Critique, serves as a good introduction to the content, if not the proofs, of Kant's critical philosophy. The Prolegomena was published between the first (A) and second (B) editions of the Critique of Pure Reason.

David Hume nearly killed metaphysics. Immanuel Kant saved it, but at a cost. In resuscitating metaphysics, Kant attempted to mend a great philosophical divide, and in doing so he created the boundaries which he believed would change the very nature of metaphysics.

For hoi polloi, metaphysics is philosophy—most picture tweed-jacketed men sitting in patent leather wing-back chairs smoking pipes and pontificating on the ultimate nature of reality. Yet for the philosopher, the term metaphysics refers to a specific study within philosophy, namely the study of problems and concepts with are beyond or transcend the physical world.

So while questions relating to the properties of iron alloys, or the growth and reproduction of Conium maculatum, are clearly grounded in the physical world of the natural sciences; questions about the existence of things outside of our consciousness, or the ultimate reasons for the existence of the universe, say many philosophers, cannot be answered by appealing to the physical world: instead one must look beyond, to metaphysics.

Metaphysics had long been the bread-and-butter of many philosophers, but the middle of the 18th century brought a strong challenge: a Scottish philosopher and historian named David Hume.

David Hume stood on one side of a very important philosophical divide that existed in both the 17th and 18th centuries. Hume, along with other philosophers like John Locke and George Berkeley, represented the empiricist camp. These philosophers tended to discount the importance of innate reasoning and logic in gaining knowledge, instead arguing that the way to discover valid knowledge was through experience and observation.

Immanuel Kant, a decade Hume's junior, started his career in philosophy occupying an opposing camp. Kant, following a tradition defined by many continental figures, chief among them Descartes and Leibniz, began as a rationalisthe felt that the way to valid human knowledge was not through experience, but instead through pure intellectual processes such as reason.

Yet Kant's rationalism was not to last: famously (at least among philosophy students) Kant wrote, “I openly confess that my remembering David Hume was the very thing which many years ago first interrupted my dogmatic slumber and gave my investigations in the field of speculative philosophy a quite new direction.”

Kant's awaking lead him to write his massive and Byzantine Critique of Pure Reason and its follow-up, Prolegomena to Any Future Metaphysics. Both of these examine the role and possibility of metaphysics, but our focus shall be Kant's simpler Prolegomena.

In his preface to the Prolegomena, Kant asks, “Whether such a thing as metaphysics be at all possible?” His answer, through the rest of the Prolegomena is, in essence, Metaphysics is possible, but not as it has been done in the past. There are boundaries, he argues, to what the study of metaphysics can uncover, but Kant ultimately concludes that with a new, critical approach the study of metaphysics is possible and can be rescued from some of Hume's criticisms.

Saving pure mathematics

First, Kant asks, “How is pure mathematics possible?” Mathematics, argues Kant, is the product of “pure reason.” More accurately, Kant categorizes pure mathematics as involving both a priori reasoning and synthetic judgments.

All forms of knowledge and reasoning, for both Kant and most other philosophers, can be divided into two forms: a priori and a posteriori. The vast majority of our knowledge—from the name of Paris Hilton's latest movie, to the number of electrons in a silver atom—can be classified as a posteriori knowledge. We know the name of Paris Hilton's movie because we've seen it, or read a review about it. We know the number of elections in a silver atom because we've consulted either a periodic table or Google. A posteriori knowledge is derived from our experiences, specifically from our experiences of sensory data regarding the world around us; in other words, I know the sky is blue because I can see that the sky is blue.

A priori knowledge, on the other hand, arises from our reasoning, logical faculties: it has nothing to do with our sensory data and personal experiences. Tautologies like “A is A” can be said to be true, no matter what experiences we've encountered—in fact one could claim that even a logical individual with no personal experiences whatsoever could know that the claim “A is A” is true. A priori knowledge obviously represents a much smaller amount of our overall knowledge.

Kant also distinguishes between two different ways of gaining knowledge. One way we can gain knowledge, according to Kant, is through analytic judgments. These analytic judgments serve to clarify knowledge we already have: they do not add any new data, they merely 'unpack' or extend the data already contained within a statement or piece of knowledge. To use a well-worn example, take the claim “all bachelors are unmarried,” this claim is, according to Kant's categorization, an analytic judgment because the claim about the martial status of bachelors in contained within the concept of the word 'bachelor'. In other words, this claim merely 'unpacks' the word bachelor into a sentence.

The claim “all bachelors eat poorly,” would be an example of a synthetic judgment. While it may be true that all bachelors eat poorly, the dietary status of all bachelors is not contained in the concept of 'the bachelor'. Instead this information is added; Kant claims that synthetic judgments add information from one of three channels. There are judgments from experience, which naturally utilize a posteriori knowledge in creating a claim. Mathematical judgments utilize a priori information about mathematical laws—Kant makes it clear that while mathematics may appear at first to fall under analytic judgments, because the results of mathematical operations come from intuitive syntheses and not from the numbers themselves, mathematical operations fall under synthetic judgments. Lastly, Kant argues there are metaphysical judgments, which are based on a priori reasoning and answer questions outside of the realm of mathematics.

We can now return to Kant's question “How is pure mathematics possible?” Kant argues that pure mathematics, which, as stated above, consists of a priori, synthetic judgments, is possible because of pure intuition. Intuition occurs when we come to a conclusion or belief about something without any logical, reasoning process to guide us there.

Imagine you meet an occasional acquaintance at a bus-stop. Immediately you think to yourself, This is Fred, the skinny, blond bachelor from work. The knowledge you have about Fred falls into two categories. The first represents our normal knowledge: you know he is named Fred because he introduced himself as such, and you know he is bachelor because Laura from accounting told you so. These pieces of knowledge come to you through discernible channels (Fred himself, or Laura from accounting) and you apply them consciously (at least theoretically consciously) to Fred as the subject.

Your knowledge that Fred is both skinny and blond is different though: it represents gained through empirical intuition, or intuition about what we perceive. Once you've met Fred and seen his hair,nobody has to tell you that he is blond, you just know, without any explicit reasoning or evidence. You never needed to learn about the qualities of the concept of 'skinniness' in order to apply the term to Fred, he simply is skinny.

Kant says that we have another type of intuition in addition to our empirical intuition: we also possess what Kant refers to as pure intuition. Our pure intuition, says Kant, exists in the form of sensibility: something like a 'filter' which proceeds our empirical perceptions, allowing us to interpret the data we receive from our senses. Naturally, because it proceeds our perceptions, this pure intuition, as the form of sensibility, is a priori: we do not need any experience to have knowledge of it.

This pure intuition comes in two very specific forms: 'time' and 'space'. Thus, argues Kant, time and space are not things-in-themselves, or in Kantian terms, noumena. Instead they are filters through which we perceive and order the phenomena, in other words, the world as it appears to us through our senses. And vitally, claims Kant, we know both the concepts of time and space a priori.

Mathematics, argues Kant, relies on the application of our pure intuition regarding time and space. Because of this, pure mathematics is possible, as it stands on firm, a priori, foundations.

Natural Science?

Next Kant turns his attention to the question, “How is pure natural science possible?” In more modern terms, Kant is asking how our knowledge regarding the physical, tangible world is 'possible'.

The potential problem Kant sees in the natural sciences, and more broadly, with our knowledge of the physical world arises because of how we perceive the world around us. According to Kant, there exists noumena, or things-in-themselves—these are objects which exist separate from us. Yet Kant argues that the noumena are distinct from what he refers to as the phenomena, or our perception of these noumena.

In simple terms, when I perceive an object, for example a bachelor, I do not have direct access to that object, which is the thing-in-itself or noumena. Instead, I merely have access to my own perceptions of that object, the phenomena or appearances of that object.

The reason Kant asks “How is pure natural science possible?” is because if we do not have direct access to the noumena, a serious problem arises: without direct access to things-in-themselves, how are we supposed to 'know' about them?

Using our senses and our empirical intuition we can, argues Kant, create subjective claims which Kant refers to as judgments of perception. Being subjective, these judgments of perception apply only to my personal experience, only to the object or objects I am directly observing, and only at the present time—they have no 'law-like' qualities.

The solution Kant proposes to this dilemma is based around a set of a priori guidelines called pure concepts of understanding. These pure concepts of understanding have general, law-like qualities and act to order our empirical experiences, into intelligible, objective universal laws. By applying these pure concepts of understanding to judgments of perception, we can create what Kant calls judgments of experience: objective bits of knowledge about our physical world.

Kant uses his pure concepts of understanding to get around many of the problems posed by Hume. While he agrees with Hume about 'cause and effect' as largely incomprehensible, saying, “Hume justly maintains that we cannot comprehend by reason the possibility of causality,” Kant also says that he is unwilling to say, as Hume does, that concepts like 'cause and effect' arise from mere habit. Instead, Kant claims, “On the contrary, I have amply shown that they and the principles derived from them are firmly established a priori before all experience.”

Ultimately Kant argues that knowledge of the physical world, in other words natural science, is 'possible' because, using pure concepts of understanding, we can create from our own subjective experiences the objective, intelligible natural laws necessary to make claims about the natural world.

What then of metaphysics?

Lastly Kant turns his attention to his original question, “Whether such a thing as metaphysics be at all possible?” His answer is somewhat mixed.

Though there are, and this is very important to Kant, strict boundaries on what metaphysics can and cannot accomplish. In this way metaphysics is different from both mathematics and natural science: both of these fields have 'limits', but within those limits any question posed can, at least in theory, be answered. But the field of metaphysics is different, argues Kant. Because we have no 'experience' regarding the questions we ask—questions which, for example, probe the nature and existence of God, or souls, or look at the origins of the Universe—we cannot come to specific conclusions regarding metaphysical questions.

But we can, claims Kant, use the boundaries of metaphysics to see what may lie beyond our realm of experience. And more importantly, we can recast the study of metaphysics into something which focuses not on broad questions which cannot be answered (due to our lack of experience), but instead focuses on critiquing reason itself.

Was he right?

The main weakness in Kant's Prolegomena to Any Future Metaphysics is Kant's argument that there can be a priori synthetic judgments using the faculty of pure intuition. Kant give pure intuition regarding space and time great importance, and in doing so allows his argument to progress from a discussion regarding the possibility of mathematics to a discussion on the possibility of metaphysics.

But Kant's assertion that pure intuition is a priori is problematic. Firstly, it is difficult, if not impossible to separate the intuitions surrounding space and time from experientially derived factors. Kant argues that space and time cannot be things-in-themselves because they are a priori, but he neglects to give a sound argument as to why both space and time must be a priori. Ultimately, this is where the major weakness in Kant's argument rests—his shifting of time and space from things-in-themselves is in my opinion brilliant, but it also is not adequately defended. Given this, I do not believe that we can whole-heartedly accept Kant's conclusions in the Prolegomena.

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