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

If in physics there's something you don't understand, you can always hide behind the uncharted depths of nature. You can always blame God. You didn't make it so complex yourself. But if your program doesn't work, there is no one to hide behind. You cannot hide behind an obstinate nature. If it doesn't work, you've messed up.

APL is a mistake, carried through to perfection.

Beware of "the real world". A speaker's apeal to it is always an invitation not to challenge his tacit assumptions.

Computer science is no more about computers than astronomy is about telescopes, biology is about microscopes or chemistry is about beakers and test tubes. Science is not about tools. It is about how we use them, and what we find out when we do.

In passing I draw attention to another English expression which often occurs in Dutch texts: "the real world". In Dutch - and I am afraid not in Dutch alone - its usage is almost always a symptom of a violent anti-intellectualism.

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