Kant reacted to the Enlightenment, to the Age of Reason, and to Newtonian mechanics (which he probably understood better than any other philosopher), by accepting determinism as a fact in the physical world, which he calls the phenomenal world. Kant's goal was to rescue the physical sciences from the devastating and unanswerable skepticism of David Hume, especially Hume's assertion that no number of "constant conjunctions" of cause and effect could logically prove causality. Kant called this assertion the "crux metaphysicorum." If Hume is right, he said, metaphysics is impossible. Kant's Critique of Pure Reason was to prove that Hume was wrong. Hume criticized the Theory of Ideas of his fellow British empiricists John Locke and George Berkeley. If, as they claim, knowledge is limited to perceptions of sense data, we cannot "know" anything about external objects, even our own bodies. But Hume said that we do have a natural belief in the external world and causal laws. Hume's idea of the mind having a "feeling" (not a reason) that leads to natural beliefs became Kant's "second Copernican revolution" that the mind projects "concepts of the understanding" and "forms of perception" on the external world.Kant put limits on what we can know by pure speculative Reason, in order to make room for Belief in a timeless noumenal (or mental) world of "analytic," a priori truths that include God, freedom, and immortality.
Kant's main change in the second edition of the Critique of Pure Reason was an attempted refutation of this British idealism (B 274). He thought he had a proof of the existence of the external world. Kant thought it a scandal in philosophy that we must accept the existence of material things outside ourselves merely as a belief, with no proof.
The only thing which might be called an addition, though in the method of proof only, is the new refutation of psychological idealism, and the strict (and as I believe the only possible) proof of the objective reality of outer intuition. However innocent idealism may be considered with respect to the essential purposes of metaphysics (without being so in reality), it remains a scandal to philosophy, and to human reason in general, that we should have to accept the existence of things outside us (from which after all we derive the whole material for our knowledge, even for that of our inner sense) merely on trust, and have no satisfactory proof with which to counter any opponent who chooses to doubt it.Martin Heidegger commented on Kant's scandal:
The 'scandal of philosophy' is not that this proof has yet to be given, but that such proofs are expected and attempted again and again.
Putting Limits on ReasonNeither Hume's Idea of "natural belief" nor Kant's "concepts of the understanding" are the apodictic and necessary truths sought by metaphysicians. They are both abstract theories about the world, whose information content is validated by experiments.
"I cannot even make the assumption − as the practical interests of morality require − of God, freedom, and immortality, if I do not deprive speculative reason of its pretensions to transcendent insight. For to arrive at these, it must make use of principles which, in fact, extend only to the objects of possible experience, and which cannot be applied to objects beyond this sphere without converting them into phenomena, and thus rendering the practical extension of pure reason impossible. I must therefore, abolish knowledge, to make room for belief."Kant's noumenal world outside of space and time is a variation on Plato's concept of Soul, Descartes' mental world, and the Scholastic idea of a world in which all times are present to the eye of God. His idea of free will is a most esoteric form of compatibilism. Our decisions are made in our souls outside of time and only appear determined to our senses, which are governed by our built-in a priori forms of sensible perception, like space and time, and built-in categories or concepts of intelligible understanding.
"We then see how it does not involve any contradiction to assert, on the one hand, that the will, in the phenomenal sphere − in visible action − is necessarily obedient to the law of nature, and, in so far, not free; and, on the other hand, that, as belonging to a thing in itself, it is not subject to that law, and, accordingly, is free."If Kant's Critique of Pure Reason can be seen as a reaction to David Hume's skeptical attitude toward knowledge that depends on sense data, the parallel between Hume and Kant is even stronger in Kant's Critique of Practical Reason. Hume and Kant both sought a reconciling of freedom and necessity or causality. Where Hume said we could not reason to knowledge of causality, for example, but could have a natural belief in causality because of our moral sentiments and feelings, so Kant claims that his Practical Reason establishes freedom in a noumenal realm whose grounding principle is morality. Freedom is the condition for the moral law.(Preface to Second Edition, Critique of Practical Reason, B XXVIII)
"Freedom, however, is the only one of all the ideas of the speculative reason of which we know the possibility a priori (without, however, understanding it), because it is the condition of the moral law which we know."In an early letter to a friend, Kant described the workings of his mind as involving chance, and in terms that sound remarkably like our Cogito model, - "The mind must...lie open to any chance suggestion which may present itself." He described his method...(Critique of Practical Reason, p.329)
"In mental labour of so delicate a character nothing is more harmful than preoccupation with extraneous matters. The mind, though not constantly on the stretch, must still, alike in its idle and in its favourable moments, lie uninterruptedly open to any chance suggestion which may present itself. Relaxations and diversions must maintain its powers in freedom and mobility, so that it may be enabled to view the object afresh from every side, and so to enlarge its point of view from a microscopic to a universal outlook that it adopts in turn every conceivable standpoint, verifying the observations of each by means of all the others."11. Letter to Marcus Herz, February 21, 1772, Werke, x, p.127
Freedom as Following Deterministic Law?
Both empiricist philosophers John Locke, George Berkeley, and David Hume, as well as rationalists like Baruch Spinoza and Gottfried Wilhelm Leibniz had great difficulties with the concept of freedom. They were all immensely influenced by the new Newtonian mechanics. The "laws of Nature" had been discovered. Confusion about freedom may have been implicit in the everyday usage of the word "free." The notion of a "freely falling stone" unconstrained by any forces on it (except that of universal gravitation) produced the concept of a free motion that was actually completely determined physically. Hobbes, for example, said that freedom was simply the absence of external constraints. For him, freedom of action is enough. Freedom of the will is a contradiction and nonsense, he thought. Kant's command of Newtonian physics was greater than Hume's admiration of it as a model for his human nature. Kant asked how we could call a man free while he is subject to physical necessity. He thought that ideas could be determined (bestimmt) by psychological forces just as the motion of matter is determined by mechanical forces.For Descartes, ideas were in a mind that is immaterial and indeterministic, and thus the seat of freedom and liberty. Why did Kant not see this possibility? Even Hume had his doubts about the assumption of universal causality. He sees clearly it implies no liberty.
how can a man be called quite free at the same moment, and with respect to the same action in which he is subject to an inevitable physical necessity?Some try to evade this by saying that the causes that determine his causality are of such a kind as to agree with a comparative notion of freedom. According to this, that is sometimes called a free effect, the determining physical cause of which lies within the acting thing itself, e. g., that which a projectile performs when it is in free motion, in which case we use the word freedom, because while it is in flight it is not urged by anything external; or as we call the motion of a clock a free motion, because it moves its hands itself, which therefore do not require to be pushed by external force; so although the actions of man are necessarily determined by causes which precede in time, we yet call them free, because these causes are ideas produced by our own faculties, whereby desires are evoked on occasion of circumstances, and hence actions are wrought according to our own pleasure. This is a wretched subterfuge ["miserable substitute" is a better translation of ein elender Behelf, but the English phrase is now famous in philosophy] with which some persons still let themselves be put off, and so think they have solved, with a petty word-jugglery [again, "a little quibbling" is better for einer kleinen Wortklauberei], that difficult problem, at the solution of which centuries have laboured In vain, and which can therefore scarcely be found so completely on the surface. In fact, in the question about the freedom which must be the foundation of all moral laws and the consequent responsibility, it does not matter whether the principles which necessarily determine causality by a physical law reside within the subject or without him, or in the former case whether these principles are instinctive or are conceived by reason, if, as is admitted by these men themselves, these determining ideas have the ground of their existence in time and in the antecedent state, and this again in an antecedent. etc. Then it matters not that these are internal; it matters not that they have a psychological and not a mechanical causality, that is, produce actions by means of ideas and not by bodily movements; they are still determining principles of the causality of a being whose existence is determinable in time, and therefore under the necessitation of conditions of past time, which therefore, when the subject has to act, are no longer in his power. This may imply psychological freedom (if we choose to apply this term to a merely internal chain of ideas in the mind), but it involves physical necessity and, therefore, leaves no room for transcendental freedom, which must be conceived as independence on everything empirical, and, consequently, on nature generally, whether it is an object of the internal sense considered in time only, or of the external in time and space. Without this freedom (in the latter and true sense), which alone is practical a priori, no moral law and no moral imputation are possible. Just for this reason the necessity of events in time, according to the physical law of causality, may be called the mechanism of nature, although we do not mean by this that things which are subject to it must be really material machines. We look here only to the necessity of the connection of events in a time-series as it is developed according to the physical law, whether the subject in which this development takes place is called automaton materiale when the mechanical being is moved by matter, or with Leibnitz spirituale when it is impelled by ideas; and if the freedom of our will were no other than the latter (say the psychological and comparative, not also transcendental, that is, absolute), then it would at bottom be nothing better than the freedom of a turnspit, which, when once it is wound up, accomplishes its motions of itself.
if voluntary actions be subjected to the same laws of necessity with the operations of matter, there is a continued chain of necessary causes, pre-ordained and pre-determined, reaching from the original cause of all to every single volition, of every human creature. No contingency anywhere in the universe; no indifference; no liberty. While we act, we are, at the same time, acted upon.Kant invented the noumenal realm (outside space and time) to make room for belief in God, freedom, and immortality. Even more important, his theory of freedom provided a basis for moral responsibility. It is sad that Kant did not see (as Descartes saw) that the mind could be the locus of the indeterminism needed to break causal chains.
Intuition and Anschauung
Kant's Critiques are not an easy read.
Statistical Regularities Imply Deterministic Laws
As early as 1784, in his Idea for a Universal History with a Cosmopolitan Intent, Kant thought that statistical regularities of social data on births, deaths, and marriages demonstrated a lack of free will in human actions as phenomena. This strange idea, that regularities seen in the distribution of random events implies an underlying deterministic law, would become very strong and influential in the works of Adolphe Quételet and Henry Thomas Buckle in the nineteenth century.
"No matter what conception may form of the freedom of the will in metaphysics, the phenomenal appearances of the will, i.e., human actions, are determined by general laws of nature like any other event of nature. History is concerned with telling about these events. History allows one to hope that when history considers in the large the play of the freedom of human will, it will be possible to discover the regular progressions thereof. Thus (it is to be hoped) that what appears to be complicated and accidental in individuals, may yet be understood as a steady, progressive, though slow, evolution of the original endowments of the entire species. Thus marriages, the consequent births and the deaths, since the free will seems to have such a great influence on them, do not seem to be subject to any law according to which one could calculate their number beforehand. Yet the annual (statistical) tables about them in the major countries show that they occur according to stable natural laws. It is like the erratic weather the occurrence of which cannot be determined in particular instances, although it never fails in maintaining the growth of plants, the flow of streams, and other of nature's arrangements at a uniform, uninterrupted pace. Individual human beings, each pursuing his own ends according to his inclination and often one against another (and even one entire people against another) rarely unintentionally promote, as if it were their guide, an end of nature which is unknown to them. They thus work to promote that which they would care little for if they knew about it. "Since men in their endeavors do not act like animals merely according to instinct, nor like rational citizens according to an agreed plan, no planned history seems to be possible (as in the case of bees and beavers). It is hard to suppress a certain disgust when contemplating men's action upon the world stage. For one finds, in spite of apparent wisdom in detail that everything, taken as a whole, is interwoven with stupidity, childish vanity, often with childish viciousness and destructiveness. In the end, one does not know what kind of conception one should have of our species which is so conceited about its superior qualities. Since the philosopher must assume that men have a flexible purpose of their own, it is left to him to attempt to discover an end of nature in this senseless march of human events. A history of creatures who proceed without a plan would be possible in keeping with such an end; the history would proceed according to such an end of nature."
Kant texts online
What Is Enlightenment?
Preface to the Second Edition of the Critique of Pure Reason
Introduction to the Second Edition of the Critique of Pure Reason
Cosmological Idea of Freedom from the Critique of Pure Reason
Critique of Pure Reason
Excerpt from the Critique of Practical Reason
Critique of Practical Reason
Critique of Judgement
Prolegomena to Any Future Metaphysics
Idea for a Universal History (1784)