All the different individuals communicate to each other the structural forms, the patterns, and they can all agree about these; but each one has to find out for himself their applicability to the world, each one has to consult his own experience, thereby giving the symbols a unique meaning, and filling the structures with content as a child may colour drawings of which only the outlines are given. And about this ineffable content they can neither agree nor disagree.
Content does not enter into science. Not on account of some imperfection of scientific knowledge, not on account of some weakness of our cognitive capacity, but simply on account of the nature of all knowledge : it is essentially a matter of structure ; he who is hungry for content is hungry for something that is utterly different from knowledge — that is all. Science is a logical structure common to all who are able to study it.
Each individual must interpret it for himself; they all agree in everything that can be expressed and tested, but we cannot even ask the question whether they agree in regard to their interpretation also, contents are essentially private and cannot be compared. But we can ask the question whether our fellow — beings always find in their own experience some content that exhibits the same structure as the one we experience in our own world. If the question has to be answered in the affirmative it simply means that we all live in one and the same world. Even a colourblind person can understand all assertions about colours and study optics just as well as any one else, although his colour perceptions have a different multiplicity from that of other people with normal eye sight. He will, for instance, imagine a sort of frame in one of his intuitive spaces so that every place in the frame will represent to him a shade of colour, and the multiplicity of all these places will correspond exactly to the multiplicity of the colour system.
By these means he will be able to find meaning in every proposition about colours and deal with it intelligently. (This method is actually in use in psychology in order to arrange all possible shades of colours in a well ordered system.)
We can never understand science and knowledge if we do not realise that the question concerning the real nature of a thing is completely and exhaustively answered by giving the structure of the thing, and there is nothing left which ought to be expressed. If you inquire into the nature of gravitations,
