The reality of the spiritual world was to me as certain as that of the physical. I felt the need, however, for a sort of justification for this assumption. I wished to be able to say to myself that the experience of the spiritual world is just as little an illusion as is that of the physical world. With regard to geometry I said to myself: “Here one is permitted to know something which the mind alone, through its own power, experiences.” In this feeling I found the justification for the spiritual world that I experienced, even as, so to speak, for the physical. And in this way I talked about this. I had two conceptions which were naturally undefined, but which played a great role in my mental life even before my eighth year. I distinguished things as those “which are seen” and those “which are not seen.”
I am relating these matters quite frankly, in spite of the fact that those persons who are seeking for evidence to prove that anthroposophy is fantastic will, perhaps, draw the conclusion from this that even as a child I was marked by a gift for the fantastic: no wonder, then, that a fantastic philosophy should also have evolved within me.
But it is just because I know how little I have followed my own inclinations in forming conceptions of a spiritual world – having on the contrary followed only the inner necessity of things – that I myself can look back quite objectively upon the childlike unaided manner in which I confirmed for myself by means of geometry the feeling that I must speak of a world “which is not seen.”
Only I must also say that I loved to live in that world For I should have been forced to feel the physical world as a sort of spiritual darkness around me had it not received light from that side.
Source: Rudolf Steiner – GA 28 – The Story of My Life – Chapter I