It is essential, if one wants to form a correct idea of what thinking is, to understand clearly that the truth of a thought in the realm to which it belongs is no evidence for its general validity. Someone can offer me a perfectly correct proof of this or that and yet it will not hold good in a sphere to which it does not belong. Anyone, therefore, who intends to occupy himself seriously with the paths that lead to a conception of the world must recognise that the first essential is to avoid one-sidedness. That is what I specially want to bring out to-day.
Source: Rudolf Steiner – GA 151 – Human and Cosmic Thought: Lecture II – Berlin, 21st January 1914
Translated by Charles Davy