principium individuationis

Just as the boatman sits in his small boat, trusting his frail craft in a stormy sea that is boundless in every direction, rising and falling with the howling, mountainous waves, so in the midst of a world full of suffering and misery the individual man calmly sits, supported by and trusting the principium individuationis, or the way in which the individual knows things as phenomena.

Arthur Schopenhauer, The World as Will and Representation, Volume I, §63, p. 353 [Dover Publications, 1966, E.F.J. Payne translation]