If people should ever start to do only what is necessary millions would die of hunger.

The "second sight" possessed by the Highlanders in Scotland is actually a foreknowledge of future events. I believe they possess this gift because they don't wear trousers.

When a book and a head collide and a hollow sound is heard, must it always have come from the book?

Nothing puts a greater obstacle in the way of the progress of knowledge than thinking that one knows what one does not yet know.

A donkey appears to me like a horse translated into Dutch.

What most clearly characterizes true freedom and its true employment is its misemployment.

The more experiences and experiments accumulate in the exploration of nature, the more precarious the theories become. But it is not always good to discard them immediately on this account. For every hypothesis which once was sound was useful for thinking of previous phenomena in the proper interrelations and for keeping them in context. We ought to set down contradictory experiences separately, until enough have accumulated to make building a new structure worthwhile.