“They became upright and taught themselves the use of tools, domesticated other animals, plants and fire, and devised language. The ash of stellar alchemy was now emerging into consciousness. At an ever-accelerating pace, it invented writing, cities, art and science, and sent spaceships to the planets and the stars. These are some of the things that hydrogen atoms do, given fifteen billion years of cosmic evolution.” -- Carl Sagan (Cosmos, 1980)

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“Empirical sciences, founded on observation of the external world, cannot aspire to completeness; the nature of things and the imperfections of our organs are alike opposed to it. We shall never succeed in exhausting the inexhaustible riches of nature, and no generation of men will ever be able to boast of having comprehended all phaenomena. It is only by distributing them into groups, that we have been able to discover in some the empires of laws, grand and simple as Nature herself.“ -- Alexander von Humboldt (Cosmos Vol. I, 1845)

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Any branch  of knowledge, cultivated by itself, not only does not suffice for itself, but presents dangers that all sensible men have recognised. Mathematics in isolation warps judgment, accustoming it to a rigor that no other science has, still less real life. Physics and chemistry obsess you by their complexity and give no breadth to the mind. Physiology leads to materialism; astronomy to vague speculation; geology turns you into a sniffing hound; literature makes you hollow; philosophy inflates you [...] You must pass from one discipline to the other so as to correct one by the other; you must cross your crops in order not to ruin the soil. -- Antonin-Dalmace Sertillanges (The Intellectual Life: Its Spirit, Condition, Methods, 1921)

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“It is one of the first duties of a professor, for example, in any subject, to exaggerate a little both the importance of his subject and his own importance in it. A man who is always asking ‘Is what I do worth while?’ and ‘Am I the right person to do it?’ will always be ineffective himself and a discouragement to others. He must shut his eyes a little and think a little more of his subject and himself than they deserve.” -- Godfrey Harold Hardy (A Mathematician's Apology, 1940)