“Although the Mathematicks according to its Etymology, signifies only Discipline, yet it merits the Name of Science better than any other, because its Principles are self-evident, and independent on any sensible Experience, and its Propositions demonstrated beyond all possible Doubt or Opposition. Youth were anciently instructed herein before Philosophy, on which Account Aristotle called it the Science of Children. This was taught them not only to raise and excite their Genius, but also as a fit preparative to the Study of Nature; and it was upon this Account that the Divine Plato inscribed on his School… that none wholly ignorant of Geometry should be admitted there.”

Subjectively speaking, the essence of philosophy is certitude; for the moderns, on the contrary, the essence of philosophy is doubt: the philosopher is supposed to reason without any premise (voraussetzungsloses Denken), as if this condition were not itself a preconceived idea; this is the classical contradiction of all relativism. Everything is doubted except for doubt. The solution to the problem of knowledge − if there is a problem − could not possibly be this intellectual suicide that is the promotion of doubt; on the contrary, it lies in having recourse to a source of certitude that transcends the mental mechanism, and this source − the only one there is − is the pure Intellect, or Intelligence as such.
[2005, The Transfiguration of Man, World Wisdom, 3, 978-0-94153219-8]
Miscellaneous, Philosophy

Language in Thought and Action, p. 271, (1939), S.I. Hayakawa

Quote attributed by Max Müller (1823–1900), Lectures on the Science of Language (2003), Kessinger Publishing, p. 238
Attributed

Source: A Mathematical Dictionary: Or; A Compendious Explication of All Mathematical Terms, 1702, p. 1, The Introduction

Source: The Prince

Attributed in posthumous publications, Einstein and Religion (1999)
Context: I have found no better expression than "religious" for confidence in the rational nature of reality as it is accessible to human reason. Wherever this feeling is absent, science degenerates into uninspired empiricism. … I cannot accept your opinion concerning science and ethics or the determination of aims. What we call science has the sole purpose of determining what is. The determining of what ought to be is unrelated to it and cannot be accomplished methodically. Science can only arrange ethical propositions logically and furnish the means for the realization of ethical aims, but the determination of aims is beyond its scope. At least that is the way I see it.

Letter to his friend Maurice Solovine (1 January 1951) p. 120

Gottfried Leibniz (May, 1686) as quoted in George R. Montgomery, Tr., "Correspondence between Leibniz and Arnauld," Leibniz: Discourse on metaphysics; correspondence with Arnauld, and Monadology https://books.google.com/books?id=5-IeAQAAMAAJ (1916) VIII, p. 108

Source: Fashionable Nihilism (2002), p. xii

"Will Mathematics Survive? Report on the Zurich Congress" in The Mathematical Intelligencer, Vol. 17, no. 3 (1995), pp. 6–10.
Context: At the beginning of this century a self-destructive democratic principle was advanced in mathematics (especially by Hilbert), according to which all axiom systems have equal right to be analyzed, and the value of a mathematical achievement is determined, not by its significance and usefulness as in other sciences, but by its difficulty alone, as in mountaineering. This principle quickly led mathematicians to break from physics and to separate from all other sciences. In the eyes of all normal people, they were transformed into a sinister priestly caste... Bizarre questions like Fermat's problem or problems on sums of prime numbers were elevated to supposedly central problems of mathematics.