On Theories (until 1799)

“Reason may be employed in two ways to establish a point: first for the purpose of furnishing sufficient proof of some principle, as in natural science, where sufficient proof can be brought to show that the movement of the heavens is always of uniform velocity. Reason is employed in another way, not as furnishing a sufficient proof of a principle, but as confirming an already established principle, by showing the congruity of its results […]” (Saint Thomas Aquinas, “Summa Theologica”, cca. 1266-1273)

“No one has yet been found so firm of mind and purpose as resolutely to compel himself to sweep away all theories and common notions, and to apply the understanding, thus made fair and even, to a fresh examination of particulars. Thus it happens that human knowledge, as we have it, is a mere medley and ill-digested mass, made up of much credulity and much accident, and also of the childish notions which we at first imbibed.” (Sir Francis Bacon, “Novum Organum” Book 2, 1620)

“We are under obligation to the ancients for having exhausted all the false theories that could be formed.” (Bernard le Bovier de Fontenelle, “Digression sur les Anciens et les Modernes", 1688)

“The moment a person forms a theory, his imagination sees, in every object, only the traits which favor that theory.” (Thomas Jefferson, [letter to Charles Thompson] 1787)