Immanuel Kant (1724-1804) was a German philosopher who was born and lived in Königsberg, Prussia. He grew up in a Lutheran Protestant household that focused on the literal interpretation of the Bible. This religious upbringing is taught through the lens of humility and devotion. He enrolled into the University of Königsberg at the age of 16, where he studied the rationalist metaphysicians of Gottfried Leibniz and Christian Wolff, and also the British mathematical science of Isaac Newton and the British empiricist philosophers. So, he was familiar with both rational idealism and empiricism during his college years. The two radically different worldviews of Leibniz and Newton were pivotal, for to throw away all scientific achievements for the sake of metaphysical speculation would be to dig his own grave, yet he recognized that one can’t simply stop doing metaphysical speculation, he believed we breathe as easily as we play metaphysics. However, metaphysics hadn’t attained a single universal or permanent knowledge claim. All metaphysicians were in contradiction to each other, and metaphysics as a science was beginning to be deeply questioned, especially in stark comparison to all the momentous achievements of Newtonian science.
After reading the philosophy of David Hume, Kant said that he was awoken from his dogmatic slumbers. He had found the friction for his own philosophy. This is how he describes Enlightenment after reading Hume:
\Enlightenment is man’s emergence from his self-incurred immaturity. Immaturity is the inability to use one’s own understanding without the guidance of another. This immaturity is self-incurred if its cause is not lack of understanding, but lack of resolution and courage to use it without the guidance of another. … Laziness and cowardice are the reasons why such a large proportion of men, even when nature has long emancipated them from alien guidance… nevertheless gladly remain immature for life. (What is Enlightenment, Nisbet Pg. 1)
Kant then set out to make possible the compatibility of the scientific achievements of his age with a new way of doing metaphysics. His aim was to show how it was possible to ground metaphysics as a science. All of Kant’s concerns can be given in three questions: What can I know? What ought I to do? What can I hope for? Many of these answers are hinted at in Kant’s final word on philosophy that came later in his life. Here he lays out the limits of philosophy:
Philosophy is not some sort of science of representations, concepts, and ideas, or a science of all sciences, or anything else of this sort; rather, it is a science of the human being, of its representing, thinking, and acting–it should present the human being in all of its components, as it is and ought to be, that is, in accordance with its natural determinations as well as its relationship of morality and freedom. … the critique of reason has appeared and determined the human being itself in the original creator of all its representations and concepts and ought to be the sole author of all its actions.
Early Modern philosophy had its set of problems, the biggest being the continuing “scandal” in philosophy, namely that which all the dominant philosophies couldn’t even prove the existence of an external world independent of one’s senses! Solipsism lurked everywhere. Descartes, Locke, Berkeley, which culminated in the great skeptic philosophy of David Hume, all came to the same conclusion that one can’t even prove the existence of the external world without doubt. Of course, Thomas Reid paved the way to defeat this nasty problem, but Kant didn’t read English and was reliant on postponing translations that weren’t always true to what the philosophers tried to convey.
Beginning in 1771 Kant contemplated on just how to reconcile metaphysics with the Science of his time. It took him ten years to build a system of philosophy, but once he understood what he must write, he took a mere 4-5 months to write his magnus opus, the Critique of Pure Reason, which he completed in 1781. However, it wasn’t well received. He compared the Critique’s arrival to that of David Hume’s own Treatise who believed it fell still born from the womb. Kant himself wrote that learning its contents was a, “disagreeable task, long winded, and dry.” In 1783 Kant wrote the Prolegomena, to Any Future Metaphysics in an attempt to make his work more accessible to teachers and students. Then he published the second edition of his Critique in 1787 that had many edits and the inclusion of a chapter called Refutation of Idealism. In the following years he published the Critique of Practical Reason which pertains to human freedom and ethics, and the Critique of Judgment which is an assessment of aesthetic taste.
Daniel N. Robinson, in his lucid book on Kant’s project How is Nature Possible? Takes on the First Critique of Pure Reason and sees within it the “highest point that transcendental philosophy can ever reach…” which is In Kant’s Prolegomena as the title to section 36: How is Nature Possible? Which is to ask how the flotsam and jetsam, that is the physical world, which impinges upon our sense organs, ever become the known and knowable world to the mind.
So on to the First Critique of Pure Reason and the Prolegomena: Kant right away agrees with Hume that all our knowledge arise from experience. We can’t know if Bill is wearing socks unless we take a look. However, Kant makes the important discovery that our experience has a grounding that should be assessed, which makes experience and understanding possible. To take a step back, we have to now ask, how is experience grounded? What woke Kant from his dogmatic slumber was specifically Hume’s theory on causation. Hume’s theory on causation can be illustrated on the billiard table. First, ball A moves, then ball B moves. That’s what causation is all about. One movement then the other movement. Hume summed up causation as, when we see one thing move, then another, it’s just a habit of the mind that A is the cause of B, a “constant conjunction” as he called it strengthens the affirmation each time the connection is witnessed.
Kant read this and had a groundbreaking moment. He thought: ball A moves, “then” ball B moves. The third term betwixt them is “then.” To make sense of this, the “then” is spatiotemporal. You can’t see time and space on the billiard table. Space and time isn’t given in experience at all. So this is the beginning of what grounds experience. From them on Kant began to build a system of metaphysics that is to be the grounding of experience itself.
Kant wanted to ground metaphysics as a science with the same foundation that mathematics and natural science had with synthetic a priori knowledge. However, there were no universal or permanent constants in metaphysics before Kant. However, with Kant’s insight into Hume’s causation theory he finally began to conceive of metaphysics as a science. Daniel N. Robinson, in his book says:
Metaphysics is not grounded in the empirical facts of the external world or the introspective facts of Cartesian-Lockean psychology. The science that is grounded in our experience of the external world is physics proper. The science that would derive its subject matter from the internal (introspectively reached) experiences is rational psychology. Metaphysics is different from both. It is an independent discipline finding its contents in that domain of a priori knowledge that is foundational for both the physical sciences and the rational psychology. There must be a conceptually prior system or science that establishes the limits of empirical knowledge and rationality alike. To the extent that such a system is possible, metaphysics itself is possible. (Robinson, How is Nature Possible? pg. 35-6).
In David Hume’s Treatise he established what is now known as “Hume’s Fork”, which consist of “relations of ideas” and “matters of fact”. Relation of ideas were ideas that were self-contained. “All bachelors are unmarried men” is a mere tautology that that term “bachelor” contains within itself. Matters of fact were statements of the world that added something empirically to the predicate. “Bill is wearing socks” is something that is gained, that the term “Bill” doesn’t necessarily contain him wearing socks, but upon looking at Bill’s feet, one then sees that he is in fact wearing socks. Kant used different terminology that would place the “relation of ideas” under the category of analytic, and “matters of fact” under the category of synthetic. But what Kant added to logic is the distinction of a priori and the a posteriori. A priori truths are known prior to experience, they give truths about words. A posteriori truths are known by experience.
Back to Kant’s wakeup call regarding Humean causation: the grounding for experience of billiard ball A moving, then, B moving is known through synthetic a priori logic. The third term betwixt them is “then” and that, the spatiotemporal framework, can’t be seen on the billiard table, so it is “pure” meaning it is not based on experience. Synthetic a priori is the grounding for all metaphysical claims Kant believes. In pure mathematics, pure natural sciences, and philosophy synthetic a priori claims are the grounding and also set a limit on what we can know in philosophy. He believed that human experience would only give us the appearance of things, or as Kant would call it the “phenomenal” realm. This phenomenal realm is where science is possible. However, we can’t perceive things as they really are in themselves, which Kant called “noumenal” realm. So there is this impenetrable barrier between the phenomenal the noumenal that humans can’t get beyond. This barrier is the limits imposed on human epistemology.
Kant claimed his arguments to be transcendent. So what does the term mean? It’s the very presuppositions on which a claim depends. In the First Critique Kant will make factual statements about thoughts and perception and then Kant presents what is the necessary grounding for the possibility for such to arise from experience. Kant, in the second edition of the Critique of Pure Reason, mentioned a Copernican revolution. He writes:
Let us, therefore, try to find out by experiment whether we shall not make better progress in the problems of metaphysics if we assume that objects must conform to our cognition… The situation here is the same as was that of Copernicus when he first thought of explaining the motion of celestial bodies. Having found it difficult to make progress there when he assumed that the entire host of stars revolved around the spectator, he tried to find out by experiment whether he might not be more successful if he had the spectator revolve and the stars remain at rest. Now, we can try a similar experiment in metaphysics, with regards to our intuition of objects. (Critique of Pure reason, Bxvi)
So what Copernicus did when he imagined himself at the center of a heliocentric solar system, placing himself where the sun is, Copernicus then was able to explain the movements of the planets accurately. So to with Kant when he has us step back and assume that it’s not experience that we should found our philosophy upon, but the pure intuitions and the pure categories of the understanding that are the root of how we sense and cogitate. But the translation of “intuition” from the German “anschaunng” may better be understood as the “outlook” or “beholding” with the sensibility. To make a table:
Transcendental Aesthetic: Allows sensibility through the pure intuitions and space and time.
Transcendental Analytic: The pure categories of the understanding, which are:
1.Categories of Quantity
2.Categories of Quality
3.Categories of Relation
Subsistence and Inherence (substance and accident)
Causality and Dependence (cause and effect)
Community (reciprocity between agent and patient)
4.Categories of Modality
Let’s talk about quantity for a moment: Now if all I had were fingers and toes, you have no trouble with quantities up to 20. You’d have no trouble with unity, or plurality, but there is nothing about the senses that can convey totality, or universality. Everyone knows that there is no number so large that you can’t add one to it. But nobody knows this by counting. No past experience will ever give one the number of infinity. Infinity isn’t a number. So, you’re probably not going to get one, you’re not going to get an infinite series by counting. It’s not a probability estimate either. Rather, the understanding has the category of quantity within it.
Now consider the categories of modality. Something is either true or false the case, or it is impossibly or possibly the case. Or its necessarily the case. If A is greater than B, and B is greater than C, then necessarily, A is greater than C. If all men are mortal, and Socrates is a man, then necessarily Socrates is mortal. With the certainties of logic and mathematics generative of necessary truths, is it not obvious that nothing in the world of sensible matter is what it is necessarily. You couldn’t possibly get the concept of necessity from sense experience! Nothing experiential in the sensible world is of such a nature that it couldn’t be different. So, the concept of necessary X can’t possibly be the gift of experience. It’s not an empirical but a pure category of the understanding.
The transcendental aesthetic allows us to experience the world. Space give us a sense of the outer world, where time gives us a sense of the inner world. The analytic is the ability to think of the world, and even conceive something beyond the possible range of experience. To have an experience at all sensation isn’t enough. The pure intuitions of time and space need to “package” experience so that it isn’t a booming, buzzing confusion, and the pure categories of the understanding then allows us to think about what is given in experience.
A good metaphor for all of this is given within a computer program, such as a web browser. With experience we see search bars, buttons that have features, we type something in and press search and it comes up with thousands of results. We don’t see the complex programming code that’s behind the scene. So to, we don’t see the pure intuitions of time and space, nor the pure categories of the understanding. Instead we see everything neatly packaged as the programmers wants us to see it so that it’s easy to operate. So what metaphysics should do is uncover what’s beneath the surface of experience, what grounds experience. The mission of metaphysics is to study what is prior to experience. Let us dive into Kant’s Prolegomena for an introduction of how metaphysics as a science is possible.
In section 1 of the Prolegomena we learn that space and time are the “form of sensibility” and allow us to connect different concepts. Concepts in the Kantian sense are what arises out of the pure categories of the understanding. The pure categories of the understanding allow us to think, the concepts are what we think about.
Metaphysical cognition must contain nothing but judgments a priori, as required by the distinguishing feature of its sources. …
Analytic judgments say nothing in the predicate except what was actually thought already in the concept of the subject… If I say: All bodies are extended, then I have not in the least amplified my concept of body, but have merely resolved it. Since extension, although not explicitly said of the former concept prior to judgment, nevertheless was actually thought of it; the judgment is therefore analytic. By contrast, the proposition: Some bodies are heavy, contains something in the predicate that is not actually though in the general concept of the body; it therefore augments my cognition, since it adds something to my concept, and must therefore be called a synthetic judgment.
b ) the common principle of all analytical judgments is the law of contradiction
c ) Synthetic judgments require a principle other than the principle of contradiction
There are synthetic judgments a posteriori whose origin is empirical; but there are also synthetic judgments that are a priori certain and that arise from pure understanding and reason…
1 . Judgments of experience are always synthetic. … That a body is extended, is a proposition that stands a priori, and not a judgment of experience. For before I go to experience, I have all the conditions for my judgment already in the concept, from which I merely extract the predicate in accordance with the principle of contradiction, and by this means can simultaneously become conscious of the necessity of the judgment, which experience could never teach me.
2 . Mathematical judgments are one and all synthetic.
First of all it must be observed: that properly mathematical propositions are always a priori and not empirical judgments, because they carry necessity with them, which cannot be taken from experience. But if this will not be granted me, very well, I will restrict my proposition to pure mathematics, the concept of which already convey that it contains not empirical but only pure cognition a priori.
One might well at first think: that the proposition 7 + 5 = 12 is a purely analytic proposition that follows from the concept of a sum of seven and five according to the principle of contradiction. However, upon closer inspection, one finds that the concept of the sum of 7 and 5 contains nothing further than the unification of the two numbers into one, through which by no means is thought what this single number may be that combines the two. The concept of twelve is in no way already thought because I merely think to myself this unification of seven and five, and I may analyze my concept of such a possible sum for as long as may be, still I will not meet with twelve therein. One must go beyond these concepts, in making use of the intuition that corresponds to one of the two, such as one’s five fingers, or five points, and in that manner adding the units of the five given in intuition step by step to the concept of seven. One therefore truly amplifies one’s concept through this proposition 7 + 5 = 12 and adds to the first concept a new one that was not thought in it; that is, an arithmetical proposition is always synthetic, which can be seen all the more plainly in the case of somewhat larger numbers, for it is then clearly evident that, though we may turn and twist our concept as we like, we could never find the sum through the mere analysis of our concepts, without making use of intuition.
Nor is any fundamental proposition of pure geometry analytic. That the straight line between two points is the shortest is a synthetic proposition. For my concept of the straight contains nothing of magnitude, but only a quality. The concept of the shortest is therefore wholly an addition and cannot be extracted by any analysis from the concept of the straight line. Intuition must therefore be made use of here, by means of which alone the synthesis is possible.
The conclusion of this section is therefore: that metaphysics properly has to do with synthetic propositions a priori, and these alone constitute its aim, for which it indeed requires many analyses of its concepts (therefore many analytic judgments), in which analyses, though, the procedure is no different from that in any other type of cognition when one seeks simply to make its concepts clear through analysis. But the generation of cognition a priori in accordance with both intuition and concepts, ultimately of synthetic propositions a priori as well, and specifically in philosophical cognition, forms the essential content of metaphysics. (pg. 22)
The Critique studies metaphysics synthetically. The Prolegomena studies it analytically. It becomes a science with the abstract examination of the concepts of pure reason and the knowledge attained thereby. Since the Prolegomena is analytically composed, it’s assuming that metaphysics is a science known through synthetic a priori propositions already.
General Question of the Prolegomena
If a metaphysics that could assert itself as science were actual, if one could say: here is a metaphysics, you need only to learn it, and it will convince you of its truth irresistibly and immutably, then this question would be unnecessary, and there would remain only that question which would pertain more to a test of our acuteness than to a proof of the existence of the subject manner itself, namely: how it is possible, and how reason should set about attaining it. Now it has not gone so well for human reason in this case. One can point to` no single book, as for instance one presents a Euclid, and say: this is metaphysics, here you will find the highest aim of this science, knowledge of a supreme being and a future life, proven from principles of pure reason. For one can indeed show us many propositions that area apodictically certain and have never been disputed; but they are one and all analytic and pertain more to the materials and implements of metaphysics than to the expansion of knowledge, which after all ought to be our real aim for it. …
Weary therefore of dogmatism, which teaches us nothing, and also of skepticism, which promises us absolutely nothing at all, not even the tranquility of a permitted ignorance; summoned by the importance of the knowledge that we need, and made mistrustful, through long experience, with respect to any knowledge that we believe we possess or that offers itself to us under the title of pure reason, there remains left for us but one critical question, the answer to which can regulate our future conduct: Is metaphysics possible at all?
[I]t happens that, even though we cannot assume that metaphysics as a science is actual, we can confidently say that some pure synthetic cognition a priori is actual and given, namely, pure mathematics and pure natural science; for both contain propositions that are fully acknowledged, agreement some as apodictically certain through bare reason, some from universal agreement with experience (though these are still recognized as independent of experience). We have therefore some at least uncontested synthetic cognition a priori, and we do not need to ask whether it is possible (for it is actual), but only: how it is possible, in order to be able to derive, from the principle of the possibility of the given cognition, the possibility of all other synthetic cognition a priori. (pg. 25-6)
How is cognition from pure reason possible?
Whether metaphysics is to stand or fall, and hence its existence, now depends entirely on the solving of this problem. … You cannot be allowed to call on the concurrence of general common sense; for that is a witness whose standing is based solely on public rumor. (pg. 28)
Here Kant underestimates Thomas Reid’s common sense. Common sense wasn’t up to “public rumor,” but it is what is universally and pragmatic necessary in the animal kingdom to march forward in life. Reid writes that the caterpillar that marches across a thousand leaves to find the one that is right for its diet, is able to do so based on principles of common sense. Kant himself uses a term that is akin to the Reidian notion of common sense which Kant coins as “mother wit.” This is how Kant describes mother with: “where mother wit is said to consist in the possession of the universal and innate rules of the understanding. (A133/B172) It’s no surprise that some of Kant’s rebuttals are the same as Reid’s since they are both answering to David Hume.
How is Pure Mathematics possible?
I call representation pure (in the transcendental sense) in which nothing is found belonging to sensation. Accordingly, the pure form of sensory intuitions in general, in which all the manifold of appearances is intuited in specific relations, will be found in the mind a priori. This pure form of sensibility will itself be called pure intuition. (A20)
[T]herefore its judgments are always intuitive, in the place of which philosophy can content itself with discursive judgments from mere concepts, and can indeed exemplify apodictic teachings through intuitions [anschauung] but can never derive them from it. This observation with respect to the nature of mathematics already guides us toward the first and highest condition of its possibility; namely, it must be grounded in some pure intuition or other, in which it can present, or, as one calls it, construct all of its concepts in concreto yet a priori. If we could discover this pure intuition and its possibility ,then from there it could easily be explained how synthetic a priori propositions are possible in pure mathematics, and consequently also how this science itself is possible; for just as empirical intuition makes it possible for us, without difficulty, to amplify (synthetically in experience) the concept we form of an object of intuition through new predicates that are presented by intuition itself, so too will pure intuition do the same, only with this difference: that in the latter case the synthetic judgment will be a priori certain, because the former only contains what is met with in contingent empirical intuition, while the latter contains what necessarily must be met with in pure intuition, since it is, as intuition a priori, inseparably bound with the concept before all experience or individual perception.
Therefore it is only by means of the form of sensory intuition that we can intuit things a priori, though by this means we can cognize objects only as they appear to us (to our senses), not as they may be in themselves; and this supposition is utterly necessary, if synthetic propositions a priori are to be granted as possible, or, in case they are actually encountered, if their possibility is to be conceived and determined in advance.
Now space and time are the intuitions upon which pure mathematics bases all its cognitions and judgements, which come forward as at once apodictic and necessary; for mathematics must first exhibit all of its concepts in intuition—and pure mathematics in pure intuition—that is, it must first construct them, failing which (since mathematics cannot proceed analytically, namely, through the analysis of concepts, but only synthetically) it is impossible for it to advance a step, that is, as long as it lacks pure intuition, in which alone the material for synthetic judgments a priori can be given. Geometry bases itself on the pure intuition of space. Even arithmetic forms its concepts of numbers through successive addition of unites in time, but above all pure mechanics can form its concepts of motion only by means of the representation of time. Both representations are, however, merely intuitions; for, if one eliminates from the empirical intuitions of bodies and their alterations (motion) everything empirical , that is, that which belongs to sensation, then space and time still remain, which are therefore pure intuitions that underlie a priori the empirical intuitions, and for that reason can never themselves be eliminated; but, by the every fact that they are pure intuitions a priori, they prove that they are mere forms of our sensibility that must precede all empirical intuition (i.e., the perception of actual objects), and in accordance with which objects can be cognized a priori, though of course only as they appear to us.
The problem of [a priori intuition] is therefore solved. Pure mathematics, as synthetic cognition a priori, is possible only because it refers to no other objects of the senses, the empirical [a posteriori] intuition of which is based on a pure and indeed a priori intuition (of space and time), and can be so based because this pure intuition is nothing but the mere form of sensibility, which precedes the actual appearance of objects, since it in fact first makes this appearance possible. This faculty of intuiting a priori does not, however, concern the matter of appearance—i.e., that which is sensation in the appearance, for that constitutes the empirical—but only the form of appearance, space and time. (pg. 35)
Kant, in his second edition of the Critique of Pure Reason, gives us the Refutation of Idealism, which he meant to be seamless. This is how Kant see the run of the mill idealisms:
Idealism (I mean material idealism) is the theory that declares the existence of the objects in space outside us either to be merely doubtful and unprovable, or to be false and impossible. The first is the problematic idealism of Descartes; it declares only one empirical assertion to be indubitable, viz.: I am. The second is the dogmatic idealism of Berkeley, it declares space, with all the tings to which space attaches as inseperable condition, to be something that is in itself impossible, and hience also declares the things in space to be mere imaginings. (B274)
Descartes wrestles with doubt due to the evil demon postulated that he attempts to defeat by mere reason when trying to prove and external world. However, problems ensue, and it could still be a dream I believe. With Berkeley there is no mind independent world. Kant himself will admit only to transcendental idealism, which is epistemological and not ontological, this is how he explains it:
By transcendental idealism of all appearances I mean the doctrinal system whereby we regard them, one and all, as mere presentations and not as things in themselves, and according to which space and time are only sensible forms of our intuition, not determinations given on their own or conditions of objects taken as things in themselves. (A369)
So, he isn’t an ordinary idealist like that of Leibniz or Berkeley, where all that exists are ideas in the mind, or that there is something leftover that the physical world can’t account for, that being “ideas.” However, for Kant there is still this barrier between the phenomenal realm of appearances and the noumenal realm of things as they really are in themselves. We can’t know the things in themselves as they really are. So, Kant’s ontology seems that there is a dual-aspect to reality. But Kant isn’t on strong feet for all he can come into contact with are the shadows of the noumenal which are the appearances of the things as they really are in themselves. He makes the logical leap that there must be a noumenal realm because he experiences the mere appearance of it that the pure intuitions pick up. He states his case here for how he turns the tables on idealism:
The proof it demands must, therefore, establish that regarding external things we have not merely imagination but also experience. And establishing this surely cannot be done unless one can prove that even our inner experience [time], indubitable for Descartes, is possible only on the presupposition of outer [space] experience. (B275)
So it is through the outer experience of what is permanent given in the intuition of space that we can have the inner experience of time. Therefore, for us to have a mental life there needs to be an external world out there that is present to the senses, and ready for the intuitions to “package,” so that we may experience anything at all. Kant drives the point home when he writes:
The mere, but empirically determined, consciousness of my own existence proves the existence of objects in space outside me. … I am conscious of my existence as fixed in time. All time determination presupposes something permanent in perception. But this permanent something cannot be something within me, precisely because my existence can be determined in time only by this permanent something. Therefore, perception of this permanent something is possible only through a thing outside me and not through my presentation of a thing outside me. Hence the determination of my existence in time is possible only through the existence of actual things that I perceive outside me. Now consciousness of my existence in time necessarily linked with consciousness of the possibility of this time determination; therefore it is necessarily linked also with the existence of things outside me, as condition of the time determination. I.e., the consciousness of my own existence is simultaneously a direct consciousness of the existence of other things outside me. (B276)
Thus, there must be an external reality that constitutes the framework of permanence, absent which, there could not be a successive, time determined life of the mind. There is still room for the skeptical claim that there might be a brain in a vat that is being sent bioelectrical signals to the brain, which fantasizes a false world unbeknownst to the “I” in the brain. Kant’s refutation of idealism is pivotal where he claims that for there to be a phenomenal world of appearances at all, then there must be a noumenal realm of things as they really are in themselves that can’t be directly seen, but are refracted in the mirrored image of the manifold of intuition. The warm, brown, bitter smell and taste that culminates in the experience of what one is holding in a cup, that which is coffee, is given in the manifold of experience, but we don’t have access to the true essence of it, only the phenomenal and not the noumenal.
James Van Cleve summarizes Kant’s theory of self most economically here:
In the philosophy of Kant, the transcendental ego is the thinker of our thoughts, the subject of our experiences, the willer of our actions, and the agent of the various activities of synthesis that help to constitute the world we experience. It is probably to be identified with our real or noumenal self (see Kant, Critique of Pure Reason, A492/B520, where “the transcendental subject” is equated with “the self proper, as it exists in itself”) . … Kant called it transcendental because he believed that although we must posit such a self, we can never observe it. (James Van Cleve, Blackwell’s Companion to Metaphysics)
To retrace the steps of how we come to have an experience that can be owned, Daniel Robinson writes:
By way of the pure intuitions of time and space, sensations are transformed into appearances. Only when these are subsumed under the pure categories of the understanding is there an experience of what is present in the external world. The necessary conditions by which there is the very possibility of experience are the pure concepts of the understanding (B161). A creature without the a priori categories could have the same sensations and appearances as we do, but not the same experiences. And the final step? The necessary concepts, through the transcendental unity of apperception, come to stand as my and your concepts. (Robinson, How is Nature Possible? pg. 151)
For Hume, what made the self is just a bundle of perception and ideas that are always in a constant state of flux marching on as we live our life. He sticks to his empirical method, which limits him from establishing what is characteristic about the permanent state of self. For Kant, the unity of apperception knits experience together to make to unify experience in to a whole.
Kant’s ethical theory can’t be overlooked either. He is a deontologist, which determines his ethical stance solely on rules. For Kant, human being act in accordance to the intelligible realm because we are rational creatures. It is only in the intelligible realm that one can act morally, and for Kant there is no higher plane of ethical will than to act according to the categorical imperative. He puts the categorical imperative two ways:
1 ) Act only according to that maxim whereby you can at the same time will that it should become a universal law.
2 ) Act as if the maxims of your action were to become through your will a universal law of nature.
Let’s take lying for example, if you lie to someone, then you are taking them out of the moral realm, and are manipulating them, and choosing for them that to live in a false world. If everyone lied, then we can’t trust a word anyone said and morality would be impossible! The world would fall apart. For our second example, let’s look at slavery. Lincoln once said, “If slavery is not wrong, nothing is wrong.” He was essentially taking a page from Kant, because to make someone a slave, you are taking them out of the moral realm where anything goes, and who is to say oneself can’t be deemed a slave next? To take one out of the moral realm is to take their freedom away, and freedom found in the intelligible realm is what makes us unique in the animal kingdom Kant believes.
Kant is usually seen as the culmination of Early Modern philosophy and it’s with him that Early Modern philosophy ends. He Is modestly empirical because he believes all knowledge arises from experience, but also a rationalist because he believes our experience is grounded in the pure intuitions and pure categories of the understanding. So, he is a synthesis between rationalism and empiricism. However hard he tries to deny being an idealist though, even over his dead body attitude, he still leaves room for idealism, because his argument isn’t seamless. Kant, like nearly all Early Modern philosophers rely on ideas, representations, appearances, and mediational theories that come between the external world and the mind. Kant believes we can’t sense the noumenal world directly, therefore, we must rely on the appearances of things, which he calls the “phenomenal” representation. He is a realist in that he believes the noumenal realm proves itself. However, because we merely gain its appearance after all, then there is still room for doubt, since there is no direct perception of the external world, and since the phenomenal realm is mere representations, Kant is restricting to mediation and the “ideal theorist” category that Thomas Reid constructed.