The light dove, cleaving the air in her free flight, and feeling its resistance, might imagine that its flight would be still easier in empty space.

Act only according to that maxim whereby you can at the same time will that it should become a universal law.

Often war is waged only in order to show valor; thus an inner dignity is ascribed to war itself, and even some philosophers have praised it as an ennoblement of humanity, forgetting the pronouncement of the Greek who said, 'War is an evil in as much as it produces more wicked men than it takes away.'

A categorical imperative would be one which represented an action as objectively necessary in itself, without reference to any other purpose.

Life is the faculty of spontaneous activity, the awareness that we have powers.

It is often necessary to make a decision on the basis of knowledge sufficient for action but insufficient to satisfy the intellect.

A science of all these possible kinds of space [the higher dimensional ones] would undoubtedly be the highest enterprise which a finite understanding could undertake in the field of geometry... If it is possible that there could be regions with other dimensions, it is very likely that God has somewhere brought them into being.