[In addition to classical, literary and philosophical studies,] I devoured without much appetite the Elements of Algebra and Geometry…. From these serious and scientific pursuits I derived a maturity of judgement, a philosophic spirit, of more value than the sciences themselves…. I could extract and digest the nutritive particles of every species of litterary food.

~~[No known source]~~ Every kind of science, if it has only reached a certain degree of maturity, automatically becomes a part of mathematics.
Eine jede Wissenschaft fällt, hat sie erst eine gewisse Reife erreicht, automatisch der Mathematik anheim.

A large proportion of mankind, like pigeons and partridges, on reaching maturity, having passed through a period of playfulness or promiscuity, establish what they hope and expect will be a permanent and fertile mating relationship. This we call marriage.

I am reminded of the great French Marshal Lyautey, who once asked his gardener to plant a tree. The gardener objected that the tree was slow-growing and would not reach maturity for a hundred years. The Marshal replied, “In that case, there is no time to lose, plant it this afternoon.”

I assume that each organism which the Creator educed was stamped with an indelible specific character, which made it what it was, and distinguished it from everything else, however near or like. I assume that such character has been, and is, indelible and immutable; that the characters which distinguish species now, were as definite at the first instant of their creation as now and are as distinct now as they were then. If any choose to maintain... that species were gradually bought to their present maturity from humbler forms... he is welcome to his hypothesis, but I have nothing to do with it.

I live in that solitude which is painful in youth, but delicious in the years of maturity.

Of all the intellectual faculties, judgment is the last to arrive at maturity. The child should give its attention either to subjects where no error is possible at all, such as mathematics, or to those in which there is no particular danger in making a mistake, such as languages, natural science, history, and so on.

Once established, an original river advances through its long life, manifesting certain peculiarities of youth, maturity and old age, by which its successive stages of growth may be recognized without much difficulty.

Our truest systems of science had small beginnings, gradual and countless contributions, and finally took their place in use, as each of you, from helpless childhood and feeble boyhood, have grown to your present strength and maturity. No such system could be born in a day. It was not as when nature in fitful pulsations of her strength suddenly lifted the land into mountain ranges, but rather, as with small accretions, gathered in during countless years, she builds her islands in the seas.

Science is the outcome of being prepared to live without certainty and therefore a mark of maturity. It embraces doubt and loose ends.

The scientist, by the very nature of his commitment, creates more and more questions, never fewer. Indeed the measure of our intellectual maturity, one philosopher suggests, is our capacity to feel less and less satisfied with our answers to better problems.

We are faced today with a social decision resulting from our progress in molecular genetics at least equal to, and probably greater than, that required of us twenty years ago with the maturity of nuclear power.

We should have positive expectations of what is in the universe, not fears and dreads. We are made with the realization that we’re not Earthbound, and that our acceptance of the universe offers us room to explore and extend outward. It’s like being in a dark room and imagining all sorts of terrors. But when we turn on the light – technology - suddenly it’s just a room where we can stretch out and explore. If the resources here on Earth are limited, they are not limited in the universe. We are not constrained by the limitations of our planet. As children have to leave the security of family and home life to insure growth into mature adults, so also must humankind leave the security and familiarity of Earth to reach maturity and obtain the highest attainment possible for the human race.

When even the brightest mind in our world has been trained up from childhood in a superstition of any kind, it will never be possible for that mind, in its maturity, to examine sincerely, dispassionately, and conscientiously any evidence or any circumstance which shall seem to cast a doubt upon the validity of that superstition. I doubt if I could do it myself.