If you can't explain what you are doing to a nine-year-old, then either you still don't understand it very well, or it's not all that worthwile in the first place.

I am enough of an artist to draw freely upon my imagination.

While it is true that science, to the extent of its grasp of causative connections, may reach important conclusions as to the compatibility and incompatibility of goals and evaluations, the independent and fundamental definitions regarding goals and values remain beyond science's reach.

That is the way to learn the most, that when you are doing something with such enjoyment that you don't notice that the time passes.

The goal of pacifism is possible only though a supranational organization. To stand unconditionally for this cause is the criterion of true pacifism.

Teaching should be such that what is offered is perceived as a valuable gift and not as hard duty. Never regard study as duty but as the enviable opportunity to learn to know the liberating influence of beauty in the realm of the spirit for your own personal joy and to the profit of the community to which your later work belongs.

We know nothing at all. All our knowledge is but the knowledge of schoolchildren. The real nature of things we shall never know.