[A comparison] of the mind of a bigot to the pupil of the eye; the more light you pour on it, the more it contracts.

Lepidoptera are for children to play with, pretty to look at, so some think. Give me the Coleoptera, and the kings of the Coleoptera are the beetles! Lepidoptera and Neuroptera for little folks; Coleoptera for men, sir!

A man may fulfill the object of his existence by asking a question he cannot answer, and attempting a task he cannot achieve.

A man of very moderate ability may be a good physician, if he devotes himself faithfully to the work.

A mind that is stretched by a new idea can never go back to its original dimensions.

A moment’s insight is sometimes worth a life’s experience.

A patent is property carried to the highest degree of abstraction—a right in rem to exclude, without a physical object or content.

As for the excellent little wretches who grow up in what they are taught, with never a scruple or a query, ... they signify nothing in the intellectual life of the race.

As knowledge advances, science ceases to scoff at religion; and religion ceases to frown on science. The hour of mockery by the one, and of reproof by the other, is passing away. Henceforth, they will dwell together in unity and goodwill. They will mutually illustrate the wisdom, power, and grace of God. Science will adorn and enrich religion; and religion will ennoble and sanctify science.

Certitude is not the test of certainty. We have been cocksure of many things that are not so.

Descartes … commanded the future from his study more than Napoleon from his throne.

Go on, fair Science; soon to thee
Shall Nature yield her idle boast;
Her vulgar lingers formed a tree,
But thou hast trained it to a post.

Go to yon tower, where busy science plies
Her vast antennae, feeling through the skies
That little vernier on whose slender lines
The midnight taper trembles as it shines,
A silent index, tracks the planets’ march
In all their wanderings through the ethereal arch;
Tells through the mist where dazzled Mercury burns,
And marks the spot where Uranus returns.

Heads I win, tails you lose.

I was just going to say, when I was interrupted, that one of the many ways of classifying minds is under the heads of arithmetical and algebraical intellects. All economical and practical wisdom is an extension or variation of the following arithmetical formula: 2+2=4. Every philosophical proposition has the more general character of the expression a+b=c. We are mere operatives, empirics, and egotists, until we learn to think in letters instead of figures.

I would never use a long word, even, where a short one would answer the purpose. I know there are professors in this country who “ligate” arteries. Other surgeons only tie them, and it stops the bleeding just as well.

It is better for all the world, if instead of waiting to execute degenerate offspring for crime, or to let them starve for their imbecility, society can prevent those who are manifestly unfit for continuing their kind. The principle that sustains compulsory vaccinations is broad enough to cover cutting Fallopian tubes. Three generations of imbeciles are enough.

It is the province of knowledge to speak and it is the privilege of wisdom to listen.

Kant … commanded the future from his study more than Napoleon from his throne.

Knowledge—it excites prejudices to call it science—is advancing as irresistibly, as majestically, as remorselessly as the ocean moves in upon the shore.

Man’s mind once stretched by a new idea, never regains its original dimension.

No man can be truly called an entomologist, sir; the subject is too vast for any single human intelligence to grasp.

O, what a precious book the one would be
That taught observers what they’re not to see!

One-story intellects, two-story intellects, three-story intellects with skylights. All fact-collectors, who have no aim beyond their facts, are one-story men. Two-story men compare, reason, generalize, using the labors of the fact-collectors as well as their own. Three-story men idealize, imagine, predict; their best illumination comes from above, through the skylight. There are minds with large ground-floors, that can store an infinite amount of knowledge; some librarians, for instance, who know enough of books to help other people, without being able to make much other use of their knowledge, have intellects of this class. Your great working lawyer has two spacious stories; his mind is clear, because his mental floors are large, and he has room to arrange his thoughts so that lie can get at them,—facts below, principles above, and all in ordered series; poets are often narrow below, incapable of clear statement, and with small power of consecutive reasoning, but full of light, if sometimes rather bare of furniture, in the attics.

Science ... in other words, knowledge—is not the enemy of religion; for, if so, then religion would mean ignorance. But it is often the antagonist of school-divinity.

Science is a first-rate piece of furniture for a man’s upper chamber, if he has common sense on the ground floor. But if a man hasn’t got plenty of good common sense, the more science he has the worse for his patient.

Science is the topography of ignorance. From a few elevated points we triangulate vast spaces, inclosing infinite unknown details. We cast the lead, and draw up a little sand from abysses we may never reach with our dredges.

The art of healing is an occupation worthy of the best and ablest men, but it is less entirely satisfying to the purely scientific mind than other pursuits of equal dignity. … A physician will have to count the pulses of thirty patients while a physiologist is watching the circulation of a single tadpole.

The crack-brained bobolink courts his crazy mate,
Posed on a bulrush tipsy with his weight.

The seer of the past was the man of mysteries. The veil within which none but the high-priest must enter, … whose traditions are the cement in which the stones of all these temples rising around us are laid. The seer of to-day is the man of explorations and explanations. Moses is busy with his microscope, and Daniel prophesies from the meteorological headquarters at Washington.

Throw out opium, which the Creator himself seems to prescribe, for we often see the scarlet poppy growing in the cornfields, as if it were foreseen that wherever there is hunger to be fed there must also be a pain to be soothed; throw out a few specifics which our art did not discover, and it is hardly needed to apply; throw out wine, which is a food, and the vapors which produce the miracle of anaesthesia, and I firmly believe that if the whole materia medica [medical drugs], as now used, could be sunk to the bottom of the sea, it would be all the better for mankind,—and all the worse for the fishes.

We can make an exception of opium “which the creator seems to prescribe, as we often see the scarlet poppy growing in the corn fields” but all other receipts of Omniscience must be condemned. The purple fox-glove, the many-tinted veratrum the lilac stramonium they are all “'noxious” but a little opium it helps the imagination.
[Criticizing the medical use of noxious psychoactive drugs.]

We must study man as we have studied stars and rocks.

Who are so rich as the poet and the man of science? “The meanest flower that blows” is an unfathomable mine of thought to the one, and “the poor beetle that we tread upon” holds a whole museum of nature’s miracles for the other.

Why have … so many … eminently furnished for professional success, seen fit to give up all their professional prospects and take the almost monastic vows of the devotee to science? Doctor Louis Agassiz, Doctor Asa Gray, Doctor Jeffries Wyman, were all duly qualified to exercise the healing art. They each left its beaten road for the several paths to which they found themselves called.

Wyman … saw where others only looked.

It was Oliver Wendell Holmes, Sr., who likened the bigot to the pupil of the human eye: the more light you expose it to the narrower it grows.

A liberal education may be had at a very slight cost of time …[with] ten books which you may make close friends.
I. Old and New Testament.
II. Shakespeare.
III. Montaigne.
IV. Plutarch’s Lives.
V. Marcus Aurelius.
VI. Epictetus.
VII. Religio Medici.
VIII. Don Quixote.
IX. Emerson
X. Oliver Wendell Holmes—Breakfast-Table Series.