"It is necessary to know the causes of things, and not only their effects, if we wish to have perfect knowledge."

"It is better to learn from the infidels than to remain in ignorance."

"The common herd of students knows nothing of the sciences, but only of words."

"The world is full of errors, and men are in darkness, and they do not know it."

"The greatest impediment to learning is the fear of error."