The World in the Head (Supplements to Book 1, Chapters 1–4)

In 1844, twenty-six years after the first volume, I published this second one. It does not replace the first. It follows the same four books, chapter by chapter, and adds what a long life of reflection has taught me. The reader should have the first volume behind him; this one is its commentary, its deepening, and in places its correction.

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Supplements to the First Book. First Half: The Doctrine of the Representation of Perception.

Chapter 1. On the Fundamental View of Idealism

In endless space there are countless shining spheres, around each of which some dozen smaller ones revolve, hot at the core and covered with a cold crust, on which a mold has produced living and knowing beings. This is the empirical truth, the real, the world. Yet for a thinking being it is a precarious position to stand on one of those countless spheres floating freely in boundless space, without knowing whence or whither, and to be only one of innumerable similar beings that crowd, press and toil, restlessly and rapidly arising and passing away in beginningless and endless time.

Here, then, idealism begins. The world, with all its spheres, exists only in a head. The realist laughs: does the world, then, live only in my brain? Is the sun in my skull? But he forgets that the "head" he is talking about is itself only something seen, a representation in another head. The world is in the head, and the head is in the world. Neither can be dropped. This is the circle in which all our knowledge moves.

Idealism does not deny the empirical reality of the world. The stone exists, the tree exists, the stars exist, in exactly the sense in which we all agree they do. What idealism denies is that this reality is the last word: that it exists as it appears, independently of any subject. A world without a subject to perceive it is a phrase without meaning, like a sound without an ear or a reflection without a mirror.

Chapter 2. On the Doctrine of Perception, or Knowledge of the Understanding

Perception is not passive. The senses deliver only raw material: a tickle in the retina, a vibration in the ear. Out of this the understanding, instantly and without our noticing, constructs a world of objects in space. It does this by referring every sensation to a cause outside us. Every act of seeing is therefore already an act of intelligence; the eye sees nothing without the brain.

This is why a man born blind, when his sight is restored, does not at once see the world. He must first learn to see, to connect sensations with causes, to judge distance and shape. And it is why the world of perception is always more than the sum of our sensations.

Chapter 3. On the Senses

The senses are only the outlets of the brain through which it receives material from outside. Sight is the most intellectual of them, the sense of the understanding; it gives us the widest and richest data, and its pleasures are the purest, because they least concern the will. Hearing is the sense of reason, for through it we receive words and therefore concepts; it is also the sense of music. Touch, smell and taste are nearer to the will, and their pleasures and pains are more bodily.

Chapter 4. On Knowledge a priori

That we know some things before all experience is the great discovery of Kant. Time, space and causality are not learned; they are the forms in which anything at all can be experienced. I have tried to show this concretely by drawing up a table of the predicates that we know a priori about time, about space and about matter. Time has only one dimension; space has three. Time cannot be perceived by itself; neither can space. Every part of time is a time, every part of space a space. Matter persists; its quantity can neither increase nor decrease. All this we know with certainty before we have looked at a single thing. And whatever we know in this way, we know because it belongs to the structure of our own intellect, not to the things themselves.

(End of Episode 1 — continued in Episode 2: Animals, Concepts and Laughter)