I have an infamously low capacity for visualizing relationships, which made the study of geometry and all subjects derived from it impossible for me.

Illusions commend themselves to us because they save us pain and allow us to enjoy pleasure instead.

I was making frequent use of cocaine at that time ... I had been the first to recommend the use of cocaine, in 1885, and this recommendation had brought serious reproaches down on me.

The more the fruits of knowledge become accessible to men, the more widespread is the decline of religious belief.

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.

The most complicated achievements of thought are possible without the assistance of consciousness.

We have become convinced that it is better to avoid such symbolic disguisings of the truth in what we tell children and not to withhold from them a knowledge of the true state of affairs commensurate with their intellectual level.