We have also obtained a glimpse of another crucial idea about languages and program design. This is the approach of statified design, the notion that a complex system should be structured as a sequence of levels that are described using a sequence of languages. Each level is constructed by combining parts that are regarded as primitive at that level, and the parts constructed at each level are used as primitives at the next level. The language used at each level of a stratified design has primitives, means of combination, and means of abstraction appropriate to that level of detail.

First, we want to establish the idea that a computer language is not just a way of getting a computer to perform operations but rather that it is a novel formal medium for expressing ideas about methodology. Thus, programs must be written for people to read, and only incidentally for machines to execute.

The computer revolution is a revolution in the way we think and in the way we express what we think. The essence of this change is the emergence of what might best be called procedural epistemology-the study of the structure of knowledge from an imperative point of view, as opposed to the more declarative point of view taken by classical mathematical subjects.

Programs must be written for people to read, and only incidentally for machines to execute.

There's a good part of Computer Science that's like magic. Unfortunately there's a bad part of Computer Science that's like religion.

Applicants must also have extensive knowledge of Unix, although they should have sufficiently good programming taste to not consider this an achievement.

The computer revolution is a revolution in the way we think and in the way we express what we think.