[Someone] remarked to me once: Physicians should not say, I have cured this man, but, This man didn’t die in my care. In physics too one might say, For such and such a phenomenon I have determined causes whose absurdity cannot finally be proved, instead of saying, I have explained it.

Non cogitant, ergo non sunt.
[They do not think, therefore they are not.]

A book is a mirror: when a monkey looks in, no apostle can look out.

A donkey looks to me like a horse translated into Dutch.

A good method of discovery is to imagine certain members of a system removed and then see how what is left would behave: for example, where would we be if iron were absent from the world: this is an old example.

A leg of mutton is better than nothing,
Nothing is better than Heaven,
Therefore a leg of mutton is better than Heaven.

A man who writes a great deal and says little that is new writes himself into a daily declining reputation. When he wrote less he stood higher in people’s estimation, even though there was nothing in what he wrote. The reason is that then they still expected better things of him in the future, whereas now they can view the whole progression.

A schoolteacher or professor cannot educate individuals, he educates only species. A thought that deserves taking to heart.

Above all things expand the frontiers of science: without this the rest counts for nothing.

According to Herr Cook's observation, the inhabitants of New Guinea have something they set light to which burns up almost like gunpowder. They also put it into hollow staves, and from a distance you could believe they are shooting. But it does not produce so much as a bang. Presumably they are trying to imitate the Europeans. They have failed to realize its real purpose.

An increase in knowledge acquired too quickly and with too little participation on one’s own part is not very fruitful: erudition can produce foliage without bearing fruit.

Astrology fosters astronomy. Mankind plays its way up.

Astronomy is perhaps the science whose discoveries owe least to chance, in which human understanding appears in its whole magnitude, and through which man can best learn how small he is.

Devised with a maximum of erudition and a minimum of common sense.

Do not say hypothesis, and even less theory: say way of thinking.

Everyone is a genius at least once a year. The real geniuses simply have their bright ideas closer together.

Everywhere in nature we seek some certainty, but all this is nothing more than an arrangement of the dark feeling of our own. All the mathematical laws that we find in Nature are always suspicious to me, despite their beauty. They give me no pleasure. They are merely expedients. Everything is not true at close range.

God created man in his own image, says the Bible; the philosophers do the exact opposite, they create God in theirs.

He had constructed for himself a certain system which thereafter exercised such an influence on his way of thinking that those who observed him always saw his judgment walking a few steps in front of his feeling, though he himself believed it was keeping to the rear.

He marvelled at the fact that the cats had two holes cut in their fur at precisely the spot where their eyes were.

Hour-glasses remind us, not only of how time flies, but at the same time of the dust into which we shall one day decay.

How might letters be most efficiently copied so that the blind might read them with their fingers?

I have often noticed that when people come to understand a mathematical proposition in some other way than that of the ordinary demonstration, they promptly say, “Oh, I see. That’s how it must be.” This is a sign that they explain it to themselves from within their own system.

I have very often reflected on what it is that really distinguishes the great genius from the common crowd. Here are a few observations I have made. The common individual always conforms to the prevailing opinion and the prevailing fashion; he regards the State in which everything now exists as the only possible one and passively accepts it ail. It does not occur to him that everything, from the shape of the furniture up to the subtlest hypothesis, is decided by the great council of mankind of which he is a member. He wears thin-soled shoes even though the sharp stones of the Street hurt his feet, he allows fashion to dictate to him that the buckles of his shoes must extend as far as the toes even though that means the shoe is often hard to get on. He does not reflect that the form of the shoe depends as much upon him as it does upon the fool who first wore thin shoes on a cracked pavement. To the great genius it always occurs to ask: Could this too not be false! He never gives his vote without first reflecting.

I imagine that when we reach the boundaries of things set for us, or even before we reach them, we can see into the infinite, just as on the surface of the earth we gaze out into immeasurable space.

I know very well the people you mean: they are all mind and theory and haven't the wit to sew on a button. Plenty of head but not hand enough to sew on a button.

I once lodged in Hanover in a room whose window gave on to a narrow Street which formed a communicating link between two bigger streets. It was very pleasant to see how people's faces changed when they entered the little Street, where they thought they were less observed; how here one pissed, there another fixed her garter, one gave way to private laughter and another shook his head. Girls thought with a smile of the night before and adjusted their ribbons for conquests in the big Street ahead.

If an angel were to tell us about his philosophy, I believe many of his statements might well sound like '2 x 2= 13'.

If it were true what in the end would be gained? Nothing but another truth. Is this such a mighty advantage? We have enough old truths still to digest, and even these we would be quite unable to endure if we did not sometimes flavor them with lies.

If we make a couple of discoveries here and there we need not believe things will go like this for ever. An acrobat can leap higher than a farm-hand, and one acrobat higher than another, yet the height no man can overleap is still very low. Just as we hit water when we dig in the earth, so we discover the incomprehensible sooner or later.

Imagine the world so greatly magnified that particles of light look like twenty-four-pound cannon balls.

In mathematical analysis we call x the undetermined part of line a: the rest we don’t call y, as we do in common life, but a-x. Hence mathematical language has great advantages over the common language.

In the republic of scholarship everybody wants to rule, there are no aldermen there, and that is a bad thing: every general must, so to speak, draw up the plan, stand sentry, sweep out the guardroom and fetch the water; no one wants to work for the good of another.

It is a good thing Heaven has not given us the power to change as much of our body as we would like to or as our theory would assert is necessary.

It is astonishing how much the word infinitely is misused: everything is infinitely more beautiful, infinitely better, etc. The concept must have something pleasing about it, or its misuse could not have become so general.

It is the geniuses who, as pioneers, create the highways, and the cultivated who level and beautify them. Highway improvement would be a good thing in the sciences, so that we could get from one of them to another more easily.

It is very much in the order of nature that toothless animals should have horns: is it any wonder that old men and women should often have them?

Libraries will in the end become cities, said Leibniz.

Man is perhaps half spirit and half matter, as the polyp is half plant and half animal. The strangest of creatures lie always at the boundary.

Many people know everything they know in the way we know the solution of a riddle after we have read it or been told it, and that is the worst kind of knowledge and the kind least to be cultivated; we ought rather to cultivate that kind of knowledge which enables us to discover for ourselves in case of need that which others have to read or be told of in order to know it.

Metaphorical language is a species of natural language which we construct out of arbitrary but concrete words. That is why it is so pleasing.

My head lies at least a foot closer to my heart than is the case with other men: that is why I am so reasonable.

Now that we know nature thoroughly, a child can see that in making experiments we are simply paying nature compliments. It is no more than a ceremonial ritual. We know the answers in advance. We consult nature in the same way as great rulers consult their parliaments.

Of all the animals on earth, man is closest to the ape.

One has to do something new in order to see something new.

Our world will yet grow so subtle that it will be as ludicrous to believe in a god as it is today to believe in ghosts.

People who have read a great deal seldom make great discoveries. I do not say this to excuse laziness, for invention presupposes an extensive contemplation of things on one's own account; one must see for oneself more than let oneself be told.

Scholars should always receive with thanks new suppositions about things, provided they possess some tincture of sense; another head may often make an important discovery prompted by nothing more than such a stimulus: the generally accepted way of explaining a thing no longer had any effect on his brain and could communicate to it no new notion.

That is as natural to man as thinking or throwing snowballs.

That man is the noblest creature may also be inferred from the fact that no other creature has yet contested this claim.

The accomplishments of those born blind are a sure proof of how much the spirit can achieve when difficulties are placed in its way.

The construction of the universe is certainly very much easier to explain than is that of the plant.

The great artifice of regarding small deviations from the truth as being the truth itself is at the same time the foundation of wit, where the whole thing would often collapse if we were to regard these deviations in a spirit of philosophical rigor.

The great rule: If the little bit you have is nothing special in itself, at least find a way of saying it that is a little bit special.

The man was such an intellectual he was of almost no use.

The more experiences and experiments accumulate in the exploration of nature, the more precarious the theories become. But it is not always good to discard them immediately on this account. For every hypothesis which once was sound was useful for thinking of previous phenomena in the proper interrelations and for keeping them in context. We ought to set down contradictory experiences separately, until enough have accumulated to make building a new structure worthwhile.

The most dangerous untruths are truths slightly distorted.

The most heated defenders of a science, who cannot endure the slightest sneer at it, are commonly those who have not made very much progress in it and are secretly aware of this defect.

The natural scientists of the previous age knew less than we do and believed they were very close to the goal: we have taken very great steps in its direction and now discover we are still very far away from it. With the most rational philosophers an increase in their knowledge is always attended by an increased conviction of their ignorance.

There are people who possess not so much genius as a certain talent for perceiving the desires of the century, or even of the decade, before it has done so itself.

There are two ways of extending life: firstly by moving the two points “born” and “died” farther away from one another… The other method is to go more slowly and leave the two points wherever God wills they should be, and this method is for the philosophers.

There are very few things of which we can acquire a conception through all five senses.

There is no greater impediment to progress in the sciences than the desire to see it take place too quickly.

To do just the opposite is also a form of imitation.

To see every day how people get the name “genius” just as the wood-lice in the cellar the name “millipede”—not because they have that many feet, but because most people don't want to count to 14—this has had the result that I don't believe anyone any more without checking.

We have to believe that everything has a cause, as the spider spins its web in order to catch flies. But it does this before it knows there are such things as flies.

What we have to discover for ourselves leaves behind in our mind a pathway that can be used on another occasion.

When one begins to speak of something it sounds plausible, but when we reflect on it we find it false. The initial impression a thing makes on my mind is very important. Taking an overall view of a thing the mind sees every side of it obscurely, which is often of more value than a clear idea of only one side of it.

When they have discovered truth in nature they fling it into a book, where it is in even worse hands.

When they saw they would never be able to set a Catholic head on his shoulders they at least struck off the Protestant one.

Where a body is in motion, there exists space and time, the simplest sentient creature in this world would thus be a measure of them. Our hearing, and perhaps our seeing too, consists of a counting of oscillations.

Why does a suppurating lung give so little warning and a sore on the finger so much?

You can be sure you are acting in accordance with the designs of nature if what you do is calculated to promote nature's great final purpose: grow and make grow. I am firmly convinced of the universality of this law.