(7) Are there parts of nature forever beyond our detection?
(8) Is the sensation which I call blue really the same as that which my neighbor calls blue? Is it possible that a blue object may arouse in him the same sensation that a red object does in me and vice versa?
(9) May there be missing integers in the series of natural numbers as we know them?
(10) Is a universe possible in which 2 + 2 ≠ 4?
(11) Why does negative electricity attract positive?
(12) Why does nature obey laws?
(13) Is a universe possible in which the laws are different?
(14) If one part of our universe could be completely isolated from the rest, would it continue to obey the same laws?
(15) Can we be sure that our logical processes are valid?
GENERAL COMMENTS ON THE OPERATIONAL POINT
OF VIEW