“Reading is thinking with someone else’s head” (Schopenhauer)

Reading is thinking with someone else’s head instead of one’s own. To think with one’s own head is always to aim at developing a coherent whole—a system, even though it be not a strictly complete one; and nothing hinders this so much as too strong a current of others’ thoughts, such as comes of continual reading. These thoughts, springing every one of them from different minds, belonging 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.

From The Art of Literature by Arthur Schopenhauer.