to different systems, and tinged with different colors, never of themselves flow together into an intellectual whole; they never form a unity of knowledge, or insight, or conviction; but, rather, fill the head with a Babylonian confusion of tongues.  The mind that is over-loaded with alien thought is thus deprived of all clear insight, and is well-nigh disorganized.  This is a state of things observable in many men of learning; and it makes them inferior in sound sense, correct judgment and practical tact, to many illiterate persons, who, after obtaining a little knowledge from without, by means of experience, intercourse with others, and a small amount of reading, have always subordinated it to, and embodied it with, their own thought.

The really scientific thinker does the same thing as these illiterate persons, but on a larger scale.  Although he has need of much knowledge, and so must read a great deal, his mind is nevertheless strong enough to master it all, to assimilate and incorporate it with the system of his thoughts, and so to make it fit in with the organic unity of his insight, which, though vast, is always growing.  And in the process, his own thought, like the bass in an organ, always dominates everything and is never drowned by other tones, as happens with minds which are full of mere antiquarian lore; where shreds of music, as it were, in every key, mingle confusedly, and no fundamental note is heard at all.

Those who have spent their lives in reading, and taken their wisdom from books, are like people who have obtained precise information about a country from the descriptions of many travellers.  Such people can tell a great deal about it; but, after all, they have no connected, clear, and profound knowledge of its real condition.  But those who have spent their lives in thinking, resemble the travellers themselves; they alone really know what they are talking about; they are acquainted with the actual state of affairs, and are quite at home in the subject.

The thinker stands in the same relation to the ordinary book-philosopher as an eye-witness does to the historian; he speaks from direct knowledge of his own.  That is why all those who think for themselves come, at bottom, to much the same conclusion.  The differences they present are due to their different points of view; and when these do not affect the matter, they all speak alike.  They merely express the result of their own objective perception of things.  There are many passages in my works which I have given to the public only after some hesitation, because of their paradoxical nature; and afterwards I have experienced a pleasant surprise in finding the same opinion recorded in the works of great men who lived long ago.