Intuition

"People have amazing facilities for sensing something without knowing where it comes from (intuition); for sensing that some phenomenon or situation or object is like something else (association); and for building and testing connections and comparisons, holding two things in mind at the same time (metaphor)." -- Robert Thurston

"When thoughts are absent, words are brought in as convenient replacements" -- Goethe (cited by Marx)

"The axiomatic basis of theoretical physics cannot be extracted from experience, but must be freely invented" -- Einstein quoted by Schwinger.