In the world outside, in so far as this world is ruled by external science, when people speak of knowledge, you will always find them say: Yes, of course, we arrive at knowledge when we have formed right judgments and exercised correct thinking. I recently cited a very simple example to illustrate how great an error is involved in this assumption that we are bound to arrive at truth when we make correct and reasonable judgments; and I would like to relate it again now, to show you that accuracy of reasoning need by no means lead to the truth.
There was once a small boy in a village who was sent regularly by his parents to fetch bread. He used always to have ten kreuzer, and bring back in exchange six rolls. If you bought one such roll it cost two kreuzer, but he always brought back six rolls for his ten kreuzer. The boy was not particularly good at arithmetic and never troubled himself as to how it worked out that he always took with him ten kreuzer, that a roll cost two and yet he brought home six rolls in return for his ten. One day a boy was brought into the family from another part and he became for our small boy a kind of foster-brother. They were of about the same age, but the foster-brother was a good arithmetician. And he saw how his companion went to the baker’s, taking with him ten kreuzer, and he knew that a roll cost two. So he said to him, “You must bring home five rolls.” He was a very good arithmetician and his reasoning was perfectly accurate. One roll costs two kreuzer (so he reasoned), he takes with him ten, he will obviously bring home five rolls. But behold, he brought back six. Then said our good arithmetician: “But that is quite wrong! One roll costs two kreuzer, and you took ten, and two into ten goes five times; you can’t possibly bring back six rolls. You must have made a mistake or else you have pinched one …” But now, lo and behold, on the next day, too, the boy brought home six rolls. It was, you see, a custom in those parts that when you bought five you received an extra one in addition, so that in fact when you paid for five rolls you received six. It was a custom that was very agreeable for anyone who needed five rolls for his household.
The good arithmetician had reasoned, quite correctly, there was no fault in his thinking; but this correct thinking did not accord with reality. We are obliged to admit the correct thinking did not arrive at the reality, for reality does not order itself in accordance with correct thinking. You may see very clearly in this case how with the most conscientious, the most clever logical thinking that can possibly be spun out, you may arrive at a correct conclusion and yet, measured by reality your conclusion may be utterly and completely false. That can always happen. Consequently a proof that is acquired purely through thought can never be a criterion for reality — never.
Source: Rudolf Steiner – GA 134 – The World of the Senses and the World of the Spirit – Hanover, 27th December 1911