... semantics ... is a sober and modest discipline which has no pretensions of being a universal patent-medicine for all the ills and diseases of mankind, whether imaginary or real. You will not find in semantics any remedy for decayed teeth or illusions of grandeur or class conflict. Nor is semantics a device for establishing that everyone except the speaker and his friends is speaking nonsense

Question: What is the difference between a “real” and a “virtual” image? Give a drawing showing the formation of one of each kind.
Answer: You see a real image every morning when you shave. You do not see virtual images at all. The only people who see virtual images are those people who are not quite right, like Mrs. A. Virtual images are things which don't exist. I can't give you a reliable drawing of a virtual image, because I never saw one.

A mathematician who can only generalise is like a monkey who can only climb UP a tree. ... And a mathematician who can only specialise is like a monkey who can only climb DOWN a tree. In fact neither the up monkey nor the down monkey is a viable creature. A real monkey must find food and escape his enemies and so must be able to incessantly climb up and down. A real mathematician must be able to generalise and specialise. ... There is, I think, a moral for the teacher. A teacher of traditional mathematics is in danger of becoming a down monkey, and a teacher of modern mathematics an up monkey. The down teacher dishing out one routine problem after another may never get off the ground, never attain any general idea. and the up teacher dishing out one definition after the other may never climb down from his verbiage, may never get down to solid ground, to something of tangible interest for his pupils.

And now the announcement of Watson and Crick about DNA. This is for me the real proof of the existence of God.

Benford's Law of Controversy: Passion is inversely proportional to the amount of real information available.

By convention sweet is sweet, by convention bitter is bitter, by convention hot is hot, by convention cold is cold, by convention colour is colour. But in reality there are atoms and the void. That is, the objects of sense are supposed to be real and it is customary to regard them as such, but in truth they are not. Only the atoms and the void are real.

I despise Birth-Control first because it is ... an entirely meaningless word; and is used so as to curry favour even with those who would first recoil from its real meaning. The proceeding these quack doctors recommend does not control any birth. ... But these people know perfectly well that they dare not write the plain word Birth-Prevention, in any one of the hundred places where they write the hypocritical word Birth-Control. They know as well as I do that the very word Birth-Prevention would strike a chill into the public... Therefore they use a conventional and unmeaning word, which may make the quack medicine sound more innocuous. ... A child is the very sign and sacrament of personal freedom. He is a fresh will added to the wills of the world; he is something that his parents have freely chosen to produce ... he is their own creative contribution to creation.

If the question were, “What ought to be the next objective in science?” my answer would be the teaching of science to the young, so that when the whole population grew up there would be a far more general background of common sense, based on a knowledge of the real meaning of the scientific method of discovering truth.

One should not understand this compulsion to construct concepts, species, forms, purposes, laws ('a world of identical cases') as if they enabled us to fix the real world; but as a compulsion to arrange a world for ourselves in which our existence is made possible:—we thereby create a world which is calculable, simplified, comprehensible, etc., for us.

Our ignorance is God; what we know is science. When we abandon the doctrine that some infinite being created matter and force, and enacted a code of laws for their government ... the real priest will then be, not the mouth-piece of some pretended deity, but the interpreter of nature.

Sir Hiram Maxim is a genuine and typical example of the man of science, romantic, excitable, full of real but somewhat obvious poetry, a little hazy in logic and philosophy, but full of hearty enthusiasm and an honorable simplicity. He is, as he expresses it, “an old and trained engineer,” and is like all of the old and trained engineers I have happened to come across, a man who indemnifies himself for the superhuman or inhuman concentration required for physical science by a vague and dangerous romanticism about everything else.

The difference between myth and science is the difference between divine inspiration of 'unaided reason' (as Bertrand Russell put it) on the one hand and theories developed in observational contact with the real world on the other. It is the difference between the belief in prophets and critical thinking, between Credo quia absurdum (I believe because it is absurd–Tertullian) and De omnibus est dubitandum (Everything should be questioned–Descartes). To try to write a grand cosmical drama leads necessarily to myth. To try to let knowledge substitute ignorance in increasingly large regions of space and time is science.

The real trouble with this world of ours is not that it is an unreasonable world, nor even that it is a reasonable one. The commonest kind of trouble is that it is nearly reasonable, but not quite. … It looks just a little more mathematical and regular than it is; its exactitude is obvious, but its inexactitude is hidden; its wilderness lies in wait.

The saying that a little knowledge is a dangerous thing is, to my mind, a very dangerous adage. If knowledge is real and genuine, I do not believe that it is other than a very valuable posession, however infinitesimal its quantity may be. Indeed, if a little knowledge is dangerous, where is a man who has so much as to be out of danger?

[S]ome physicists describe gravity in terms of ten dimensions all curled up. But those aren't real words—just placeholders, used to refer to parts of abstract equations.

[The purpose of flight research] is to separate the real from the imagined problems and to make known the overlooked and the unexpected.