There are four powers: memory and intellect, desire and covetousness. The two first are mental and the others sensual. The three senses sight, hearing, and smell cannot well be prevented; touch and taste not at all.

Anyone who conducts an argument by appealing to authority is not using his intelligence; he is just using his memory.

If you find from your own experience that something is a fact and it contradicts what some authority has written down, then you must abandon the authority and base your reasoning on your own findings.

Just as food eaten without appetite is a tedious nourishment, so does study without zeal damage the memory by not assimilating what it absorbs.

Those who, in debate, appeal to their qualifications, argue from memory, not from understanding.

The acquisition of knowledge is always of use to the intellect, because it may thus drive out useless things and retain the good. For nothing can be loved or hated unless it is first known.