Progress is possible only if we train ourselves to think about programs without thinking of them as pieces of executable code.

Simplicity is prerequisite for reliability.

The purpose of abstraction is not to be vague, but to create a new semantic level in which one can be absolutely precise.

We shall do a much better programming job, provided that we approach the task with a full appreciation of its tremendous difficulty, provided that we stick to modest and elegant programming languages, provided that we respect the intrinsic limitations of the human mind and approach the task as Very Humble Programmers.

The tools we use have a profound and devious influence on our thinking habits, and therefore on our thinking abilities.

LISP has jokingly been described as "the most intelligent way to misuse a computer." I think that description is a great compliment because it transmits the full flavour of liberation: it has assisted a number of our most gifted fellow humans in thinking previously impossible thoughts.