1.
It has sometimes been said that we find nowhere in nature an analogue of the difference between happens and is, on the one hand, and ought, on the other hand.
Wolfgang Kohler
5.
If we wish to imitate the physical sciences, we must not imitate them in their contemporary, most developed form; we must imitate them in their historical youth, when their state of development was comparable to our own at the present time. Otherwise we should behave like boys who try to copy the imposing manners of full-grown men without understanding their raison d' être, also without seeing that in development one cannot jump over intermediate and preliminary phases.
Wolfgang Kohler