Opposition is not necessarily enmity; it is merely misused and made an occasion for enmity.

We should picture the instrument that carries our mental functioning as resembling a compound microscope or photographic apparatus.

An unrestricted satisfaction of every need presents itself as the most enticing method of conducting one's life, but it means putting enjoyment before caution, and soon brings its own punishment.

The view is often defended that sciences should be built up on clear and sharply defined basal concepts. In actual fact no science, not even the most exact, begins with such definitions. The true beginning of scientific activity consists rather in describing phenomena and then in proceeding to group, classify and correlate them.

The price of civilization is instinctual renunciation.

Indeed, the great Leonardo (da Vinci) remained like a child for the whole of his life in more than one way. It is said that all great men are bound to retain some infantile part. Even as an adult he continued to play, and this was another reason why he often appeared uncanny and incomprehensible to his contemporaries.

The assumption that everything past is preserved holds good even in mental life only on condition that the organ of the mind has remained intact and that its tissues have not been damaged by trauma or inflammation. But destructive influences which can be compared to causes of illness like these are never lacking in the history of a city, even if it has had a less chequered past than Rome, and even if, like London, it has hardly ever suffered from the visitations of an enemy.