「為学日益，為道日損．」
     （学を為すは日に益す，道を為すは日に損ず．） 

                         -- 老子，道徳経，第４８章，約紀元前６００年.


     「知彼知己，勝乃不殆；知天知地，勝乃可全．」
     （彼れを知りて己れを知れば，勝乃ち殆うからず；
     　地を知りて天を知れば、勝乃ち全うすべし．） 

                         -- 孫子，孫子兵法，第１０篇，約紀元前５００年.


     "Logic is the science of sciences, and the art of arts."

                         -- John Duns Scotus, 13th century.


     "Knowledge is power."

                         -- Francis Bacon, 1598.


     "The art of discovery may advance as discoveries advance."

                         -- Francis Bacon, 1620.


     "In mathematics the art of proposing a question
      must be held of higher value than solving it."

                         -- Georg Ferdinand Ludwig Philipp Cantor, 1867.


     "As long as a branch of science offers an abundance of problems,
      so long is it alive: a lack of problems foreshadows extinction or
      the cessation of independent development."

                         -- David Hilbert, 1900.


     "The formulation of a problem is often more essential than its solution,
      which may be merely a matter of mathematical or experimental skill.
      To raise new questions, new possibilities,
      to regard old problems from a new angle,
      requires creative imagination and marks real advance in science."

                         -- Albert Einstein, 1938.


     "The best theory is inspired by practice and 
      the best practice is inspired by theory."

                         -- Donald E. Knuth, 1989.