It is not when truth is dirty, but when it is shallow, that the lover of knowledge is reluctant to step into its waters.

I believe there exists, & I feel within me, an instinct for the truth, or knowledge or discovery, of something of the same nature as the instinct of virtue, & that our having such an instinct is reason enough for scientific researches without any practical results ever ensuing from them.

On the mountains of truth you can never climb in vain: either you will reach a point higher up today, or you will be training your powers so that you will be able to climb higher tomorrow.

The libraries of America are and must ever remain the home of free and inquiring minds. To them, our citizens - of all ages and races, of all creeds and persuasions - must be able to turn with clear confidence that there they can freely seek the whole truth, unvarnished by fashion and uncompromised by expediency.

We have no organ at all for knowledge, for truth: we know (or believe or imagine) precisely as much as may be useful in the interest of the human herd, the species: and even what is here called usefulness is in the end only a belief, something imagined and perhaps precisely that most fatal piece of stupidity by which we shall one day perish.

Books are infinite in number and time is short. The secret of knowledge is to take what is essential. Take that and try to live up to it.