The Seven World Riddles
In 1880 du Bois-Reymond delivered a famous speech to the Berlin Academy of Sciences defining seven "world riddles," some of which, he declared, neither science nor philosophy could ever explain. These "riddles" or "shortcomings" of science are as follows:
1: the ultimate nature of matter and force,
2: the origin of motion,
3: the origin of life,
4: the "apparently teleological arrangements of nature," not an "absolutely transcendent riddle,"
6: the origin of simple sensations, "a quite transcendent" question,
7: the origin of intelligent thought and language, which might be known if the origin of sensations could be known, and
the question of free will.
Concerning numbers 1, 2 and 5 he proclaimed: "Ignoramus" (we will never know).