Pure Mathematics is the class of all propositions of the form "p implies q," where p and q are propositions containing one or more variables, the same in the two propositions, and neither p nor q contains any constants except logical constants. And logical constants are all notions definable in terms of the following: Implication, the relation of a term to a class of which it is a member, the notion of such that, the notion of relation, and such further notions as may be involved in the general notion of propositions of the above form. In addition to these, mathematics uses a notion which is not a constituent of the propositions which it considers, namely the notion of truth.

Again, in regard to actual human existence, I have found myself giving honour to those who feel its tragedy, who think truly about Death, who are oppressed by ignoble things even when they are inevitable; yet these qualities appear to me to militate against happiness, not only to the possessors, but to all whom they affect. And, generally, the best life seems to me one which thinks truly and feels greatly about human things, and which, in addition, contemplates the world of beauty and of abstract truths. This last is, perhaps, my most anti-utilitarian opinion: I hold all knowledge that is concerned with things that actually exist – all that is commonly called Science – to be of very slight value compared to the knowledge which, like philosophy and mathematics, is concerned with ideal and eternal objects, and is freed from this miserable world which God has made. [Utilitarians] have been strangely anxious to prove that the life of the pig is not happier than that of the philosopher – a most dubious proposition...

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It seems to me now that mathematics is capable of an artistic excellence as great as that of any music, perhaps greater; not because the pleasure it gives (although very pure) is comparable, either in intensity or in the number of people who feel it, to that of music, but because it gives in absolute perfection that combination, characteristic of great art, of godlike freedom, with the sense of inevitable destiny; because, in fact, it constructs an ideal world where everything is perfect and yet true.

[Unlike the] utilitarian... I judge pleasure and pain to be of small importance compared to knowledge, the appreciation and contemplation of beauty, and a certain intrinsic excellence of mind which, apart from its practical effects, appears to me to deserve the name of virtue. [For] many years it seemed to me perfectly self-evident that pleasure is the only good and pain the only evil. Now, however, the opposite seems to me self-evident. What first turned me away from utilitarianism was the persuasion that I myself ought to pursue philosophy, although I had (and have still) no doubt that by doing economics and the theory of politics I could add more to human happiness. It appeared to me that the dignity of which human existence is capable is not attainable by devotion to the mechanism of life, and that unless the contemplation of eternal things is preserved, mankind will become no better than well-fed pigs. But I do not believe that such contemplation on the whole tends to happiness. It gives moments of delight, but these are outweighed by years of effort and depression.

Pure mathematics consists entirely of assertions to the effect that, if such and such a proposition is true of anything, then such and such another proposition is true of that thing. It is essential not to discuss whether the first proposition is really true, and not to mention what the anything is, of which it is supposed to be true. Both these points would belong to applied mathematics. We start, in pure mathematics, from certain rules of inference, by which we can infer that if one proposition is true, then so is some other proposition. These rules of inference constitute the major part of the principles of formal logic. We then take any hypothesis that seems amusing, and deduce its consequences. If our hypothesis is about anything, and not about some one or more particular things, then our deductions constitute mathematics. Thus mathematics may be defined as the subject in which we never know what we are talking about, nor whether what we are saying is true. People who have been puzzled by the beginnings of mathematics will, I hope, find comfort in this definition, and will probably agree that it is accurate.

Thee might observe incidentally that if the state paid for child-bearing it might and ought to require a medical certificate that the parents were such as to give a reasonable result of a healthy child – this would afford a very good inducement to some sort of care for the race, and gradually as public opinion became educated by the law, it might react on the law and make that more stringent, until one got to some state of things in which there would be a little genuine care for the race, instead of the present haphazard higgledy-piggledy ways.

I am looking forward very much to getting back to Cambridge, and being able to say what I think and not to mean what I say: two things which at home are impossible. Cambridge is one of the few places where one can talk unlimited nonsense and generalities without anyone pulling one up or confronting one with them when one says just the opposite the next day.

I should like to believe my people's religion, which was just what I could wish, but alas, it is impossible. I have really no religion, for my God, being a spirit shown merely by reason to exist, his properties utterly unknown, is no help to my life. I have not the parson's comfortable doctrine that every good action has its reward, and every sin is forgiven. My whole religion is this: do every duty, and expect no reward for it, either here or hereafter.