From Kant's definition of analytic and synthetic truths to probe the limits of human understanding, down to Freud's psychoanalysis and the id, ego and super-ego, Roger Scruton presents a summary of abstract thought from the 18th century to the present day.
or thinkers who dealt in abstract ideas, the Enlightenment had a meaning over and above the scientific revolution and the rise of democratic politics. It signified a retreat from the belief that the meaning of the world is to be found in theology and the "God's-eye view". Such a view, in the eyes of the Enlightenment, is unobtainable. If the world has a meaning, therefore, it lies in the human mind and the human heart. For Immanuel Kant and his romantic followers the world was first seen as our world, and then as my world, and I myself finally dissolved into pure "spirit" (G. W. F. Hegel), "subjectivity" (S?ren Kierkegaard) or "will" (Artur Schopenhauer).
Right through to modern times, with the phenomenology of Husserl, the Freudian theory of the unconscious and the existentialist idea of freedom, the "I" remained centre-stage. The history of philosophy in modern times has really been the story of the "self". Being the subject and not the object of awareness, the self can never be observed. Yet nothing indescribable has provoked so many descriptions.
Kant's philosophy of the self comes at the end and not at the beginning of his argument. It is now usual to allow him the supreme place among modern philosophers, not merely on account of his influence, but also because his system may, for all we know, be the right one. According to Kant, there are limits to human understanding, beyond which we cannot think coherently. Moreover, we can know what those limits are, and hence draw a boundary to the knowable world. At the same time, he argued, the thought of a world beyond human understanding - a world of "things in themselves" - is meaningful.
Kant distinguishes a priori from a posteriori truth. The first is self-validating, and known by reasoning; the second is known only through experience. Among a priori truths Kant distinguishes the analytic from the synthetic. An analytic truth is true by virtue of the meaning of the words used to express it, for example, the truth that all women are female.
Synthetic a priori truths are not, in this way, "matters of definition", but substantial discoveries: discoveries that come to us through thinking. Metaphysics, Kant argues, is a science of synthetic a priori truths. But how is such a science possible? The great system builders (for example, Spinoza and Leibniz) assumed that we can know the world by pure reason, as it is in itself. But they neglected to ask the crucial question: what validates their arguments? How is synthetic a priori knowledge possible? The system builders do not say.
In his Critique of Pure Reason, Kant sets out to answer the question. First he argues that synthetic a priori knowledge exists and that mathematics is an example. He then uses this example to suggest a general theory. If we can know the truths of arithmetic and geometry, he suggests, this must be because they record features of our own perspective. In studying mathematical truths we are not looking out on the world beyond but, as it were, tracing the frame through which we perceive it. That is why we do not need to consult experience to prove them.
Metaphysics also offers examples of truths known by reason. The understanding, Kant argued, is endowed with certain concepts - such as substance, cause and quantity - which impose order on our experience and make it intelligible. These concepts can be applied only on the assumption that experience "conforms" to them. This means that the world must present a systematic appearance, in which objects endure through change, in which causal connections are universal, and in which everything happens in a law-governed way. This appearance is the condition under which anything whatsoever can be known, including ourselves. I can have knowledge of myself and my experiences only on the assumption that I inhabit an objective and law-governed order of things. This assumption must be made even by the person who denies it; hence it is true.
The human understanding can advance to the limits of human experience. There is a permanent temptation, however, to pass beyond those limits, to seek knowledge of the world from a "transcendental" perspective. That is the temptation of "pure reason", which Kant argues leads only to illusion. He demolishes the traditional theories about the self, the world, God and freedom; he tells us that which we can never know through pure reason, we can divine in another way. In practical reason we are presented with another view of our condition, and from this perspective we can know -not as a theoretical truth, but as an intuitive datum - that we are free, immortal and living under the jurisdiction of a benign moral order.
Kant writes of the "faculties" of the human mind, distinguishing the legitimate from the illegitimate use of them, and trying to show their deep interconnection. This makes it look as though his philosophy is really a kind of "deep psychology", and for a while that was how it was understood. J. G. Fichte looked for the faculty that Kant said no human but only God could possess, "intellectual intuition", which understands the world abstractly but immediately, as though idea and sensation were one. According to Fichte we do have an intellectual intuition, namely of the self. The self intuits itself by "positing" itself as an object of knowledge. This word "posit" (German setzen) contains the essence of post-Kantian idealism. For Fichte and his followers, all knowledge, all understanding and all experience involves an act of the mind, whereby the object is presented to consciousness. Since we actively posit the object of knowledge, the object is not in the end distinct from us. The world is ideal, and if it were not ideal it would not be knowable.
Fichte remade the Kantian philosophy as a kind of drama: the self posits the object of knowledge, which, being an object, not a subject, is known only as "not-self". Every venture outwards towards the object is also an alienation of the self. We can achieve freedom and self-knowledge only through this process of alienation or self-sundering, which we overcome at last when we achieve the "intellectual intuition" of the self in its wholeness.
That picture survives in the greatest of Kant's successors, Hegel, who made metaphysical idealism into the cornerstone of German academic philosophy. The Kantian philosophy, Hegel argued, tried to justify our claims to knowledge by showing that our faculties are inherently directed to the truth. But this "deduction" of our faculties proceeds by means of them, and therefore presupposes precisely what it aims to prove. There can be no non-circular justification of our rational powers: all that philosophy can do is to engage in a continuous critique of knowledge, and so ascend to an ever higher standpoint as the imperfections of each partial cognition are overcome. Nevertheless, by this very process, philosophy can reach the perspective (the Absolute Idea) where knowledge, being complete, vindicates itself.
This ascent of philosophy towards the Absolute is the dialectic, and it is mirrored in every sphere of human endeavour. The dialectic proceeds by the "labour of the negative". In thinking, for example, a concept is first "posited" and then negated by its "determination", as when I distinguish the table before me from that which is not the table, and so give a determinate outline to the object of knowledge. Hegel discerns a contradiction here, between the concept and its negation, and argues that this contradiction can be resolved only by transcending my imperfect knowledge to a higher and truer conception of things. Only at the highest level of all, the Absolute Idea, are the contradictions in human knowledge overcome.
The dialectic has often been dismissed as mumbo-jumbo; but it inspired Hegel to look for its signs in all human institutions. He believed that history also proceeds by dialectical steps, each stage being contradicted from within by the seeds of its successor, and the whole advancing by inexorable logic towards the final state of absolute freedom and absolute knowledge, as man emancipates himself from his infancy. The broad picture is absurd; but the brilliance of Hegel's observations made his lectures on the philosophy of history into the 19th century's most influential book, and one whose influence has been equally welcomed and deplored.
The main channel through which this influence flowed was Karl Marx. He belonged to the group of "Left Hegelians", led by Bruno Bauer and Ludwig Feuerbach, who sought to use Hegel's philosophy to overthrow his politics. Hegel was a conservative and a defender of the Prussian state, of bourgeois civilisation, of private property and of the institutions of religion. Marx and his associates believed that Hegel's picture of the human condition lent itself more plausibly to radical socialist politics. According to Hegel, spirit (the human essence) exists first in an "immediate" form, without self-knowledge or freedom, but essentially unified and at home with itself. Its final "realisation" is achieved by a return to unity, but in a condition of achieved self-knowledge. To reach this final point, spirit must pass through a long trajectory of separation, sundered from its home, and struggling to affirm itself in a world that it does not control. This state of "alienation" (Entfremdung) is the realm of becoming, in which consciousness is separated from its object and from itself. Hegel had justified private property as part of the subject's bid for freedom, part of his attempt to win a place for himself in an objective order and to claim sovereignty over his world. Marx counters by saying that, in that case, private property is part of the alienation of the subject, part of what must be overcome if the subject is to be "restored to himself". Under the regime of private property, Marx argued, man exists in servitude, forced to treat himself as an exchangeable commodity in a world where everything, including human life, is a means only, never an end in itself.
Before completing this Hegelian refutation of Hegel, Marx underwent a conversion to the empiricist economics of Adam Smith and David Ricardo. He thereafter sought to rewrite his critique of private property and of the system of "capital" (a term derived from the French utopian socialist, Saint-Simon) in the form of a social science. In doing so he revived Hegel's theory of history, in a new and "materialist" version. Hegel had seen history as motivated by the spirit's need to realise itself. For Marx the real motor of history is not spirit but the material forces of "production". Each period of history owes its character to the economic relations that prevail in it; and each gives way to the next when the forces of production burst through these economic relations and precipitate an era of revolutionary change. Capitalism emerged in this way from feudalism, and will give way to the communist phase of human development, when man will have achieved mastery over nature, and private property will no longer be useful. Laws and institutions do not cause social change, but are caused by it. They form part of the "superstructure" of society, and exist only so long as they serve the purposes of the economic "base". As soon as economic conditions enter the period of revolutionary change, all institutions are swept away in the turmoil.
That picture of human history manifests the vice that Schopenhauer called "unscrupulous optimism", a vice everywhere to be found in the Hegelians, whom he detested. Schopenhauer urged a return to Kant's "transcendental idealism", according to which every object is known only under the conditions which make knowledge possible - in other words, every object is conditioned by the subject. The world is mere "representation", and its outlines are given by the concepts of space, time and causality. The underlying reality is that thing which we discover in ourselves, and which cannot be known through concepts: namely will.
Equally opposed to the Hegelian system, was Kierkegaard, inventor of the term "existentialism", who advocated a "leap of faith" into the unknown. According to Kierkegaard, I exist as a concrete and freely choosing agent, for whom all truth is "subjectivity, ie my truth. This was his way of defending the Christian religion against science on the one hand and Hegelian mumbo-jumbo on the other. And stated thus abstractly, it is not much of a defence.
The paradoxical emphasis on the subject and his absolute right to his own standard of truth reappears in the philosophy of Friedrich Nietzsche, who used it to attack the Christian religion rather than to defend it. "There are no truths," he wrote, "only interpretations." The aim of thinking is not truth but power. We must therefore distinguish those systems of philosophy that confer power on the weaker specimens, from those that release what is strongest in us, and enable us to rise to the higher plane of the Superman (ubermensch). Since God is dead, nothing can impede me in this save my own inherent weakness and the resentment of my inferiors.
A far cry from Nietzsche is the moral philosophy that had greatest impact in Victorian England - the utilitarianism of Jeremy Bentham and John Stuart Mill. This tells us that both law and morality are justified in terms of the happiness that they bring. "The greatest happiness of the greatest number" is the goal of human institutions. Mill defended utilitarianism, but he did not really believe in it. His real mark was made by his account of liberty, and by his view that we are justified in restricting the freedom of the individual only if others would be harmed if we did not do so. His influence over subsequent political and ethical thinking was enormous, but his greatest work, on logic and the philosophy of science, was noticed only by academic specialists.
The development of logic is, however, one of the great intellectual success stories of the 19th century, and its culmination in the attempts of Gottlob Frege and Bertrand Russell to derive mathematical from logical truth deserves far more attention than anything by Marx or Nietzsche. However, this intellectual achievement arouses little interest outside the academy. The tradition which began with Frege is sometimes known as "analytical" philosophy, since it focuses on the analysis of concepts. There emerged from the analytical movement a philosopher who has aroused the curiosity of the wider reading public, Ludwig Wittgenstein, who was in fact concerned with the same broad questions as Kant.
For Wittgenstein, the limits of thought are the limits of language, and we can therefore understand the contours of our world by exploring what can and cannot be said about it. Language, however, does not work in a single or simple way - we play a variety of "language games", whose rules vary. In all instances, however, language is a public phenomenon. He even argues that there can be no such thing as a rule-guided activity accessible to one person alone. There can be no private language, and hence philosophies that imagine the self as communing with itself in isolation must be rejected. Wittgenstein was interested in the distinctive features of the human mind, such as will, self-consciousness, aesthetic experience, hope and expectation. His account was not without precedent. There is another tradition of modern philosophy, normally known as phenomenology, that anticipated some of his results. This originated with the work of the Kantian Wilhelm Dilthey, and Franz Brentano. Their suggestions were taken up by Edmund Husserl, who believed that no mental phenomenon could be studied if we did not first "bracket" all reference to external things, so as to arrive at what is purely "given" to consciousness in the act of introspection. In this way we discover the essence of every mental state, the "horizon of potentiality" that is grasped when all contamination of the actual has been thought away. The idea was taken up by his pupil, Martin Heidegger (1889-1976). The study of phenomena, he argued, leads us to the fundamental question of metaphysics, which is the "question of being". This question has "ontological priority" over all other questions, which is to say, not merely that all other questions must wait on it for an answer, but that we too depend on that answer. My existence is at stake in the question, and I find the answer by existing in another way. Thus Heidegger stumbled on the attitude celebrated by Kierkegaard: the attitude of "existentialism", which places individual existence before every attempt at objective knowledge.
Not many people have felt confident that they understand Heidegger's philosophy of existence. Nevertheless, it had an enormous impact on the thought of Jean-Paul Sartre, who did most to create the intellectual atmosphere of postwar Europe, and to prepare the way for the inglorious revolution of 1968. According to Sartre, the essence of the human condition is freedom: I am what I choose to be, and am nothing until I have chosen. But my freedom is everywhere threatened. I live as a subject among objects, and the danger is that I might "fall" into that world of objects, and become one with them. In reaction, I may hide from myself, bury myself in some predetermined role, so crossing the chasm that divides me from objects only to become an object myself. This happens, he says, when I adopt a morality, a religion or a social role that has been devised for me by others, and which has significance for me only as far as I am objectified in it. Sartre called the result "bad faith", Heidegger "inauthenticity".
Sartre's exploration of this condition brings him into conflict with the figure who has had the greatest hidden influence on the mental and moral philosophy of this century, the founder of psychoanalysis, Sigmund Freud. For Freud the most important and influential parts of the human mind are unconscious; I am what I am, not through my conscious choices but through the workings of forces accumulated during childhood. In later life, the feelings that well up from the unconscious are transferred on to other objects, and so determine the erotic and personal history of the subject. Freud suggested the compartmentalisation of the mind, which allegedly contains the unconscious id, the conscious ego, and the overseeing super-ego, implanted by our experience of repression, which forces emotions to conceal themselves and allows them also to emerge. Freud's vision of the human mind is a bundle of metaphors, and few philosophers accept it. But it raises the question that all late 20th-century thinkers must face: namely, how do we reconcile the results of philosophy, with its abstract and a priori vision of our condition, with the advance of science, which treats the human mind as one natural object among many? That is also the question that troubled Kant. And perhaps we are still no nearer to an answer.l Roger Scruton is visiting professor of philosophy at Birkbeck College, University of London.