As the biggest library if it is in disorder is not as useful as a small but well-arranged one, so you may accumulate a vast amount of knowledge but it will be of far less value to you than a much smaller amount if you have not thought it over for yourself; because only through ordering what you know by comparing every truth with every other truth can you take complete possession of your knowledge and get it into your power. You can think about only what you know, so you ought to learn something; on the other hand, you can know only what you have thought about.
Monotheistic religions alone furnish the spectacle of religious wars, religious persecutions, heretical tribunals, that breaking of idols and destruction of images of the gods, that razing of Indian temples and Egyptian colossi, which had looked on the sun 3,000 years: just because a jealous god had said, Thou shalt make no graven image.
It would be better if there were nothing. Since there is more pain than pleasure on earth, every satisfaction is only transitory, creating new desires and new distresses, and the agony of the devoured animal is always far greater than the pleasure of the devourer
Reason deserves to be called a prophet; for in showing us the consequence and effect of our actions in the present, does it not tell us what the future will be?
Of all the intellectual faculties, judgment is the last to mature. A child under the age of fifteen should confine its attention either to subjects like mathematics, in which errors of judgment are impossible, or to subjects in which they are not very dangerous, like languages, natural science, history, etc.
alent is like the marksman who hits a target which others cannot reach; genius is like the marksman who hits a target, as far as which others cannot even see.
Optimism is not only a false but also a pernicious doctrine, for it presents life as a desirable state and man's happiness as its aim and object. Starting from this, everyone then believes he has the most legitimate claim to happiness and enjoyment. If, as usually happens, these do not fall to his lot, he believes that he suffers an injustice, in fact that he misses the whole point of his existence.