In order to assist the checker, the programmer should make assertions about the various states that the machine can reach.

the programmer should make a number of definite assertions which can be checked individually, and from which the correctness of the whole programme easily follows.

The price of reliability is the pursuit of the utmost simplicity. It is a price which the very rich find most hard to pay.

If our basic tool, the language in which we design and code our programs, is also complicated, the language itself becomes part of the problem rather than part of its solution.

A feature which is omitted can always be added later, when its design and its implications are well understood. A feature which is included before it is fully understood can never be removed later.

I conclude that there are two ways of constructing a software design: One way is to make it so simple that there are obviously no deficiencies and the other way is to make it so complicated that there are no obvious deficiencies.

we recognized that a subset could be an improvement on the original.

First, we certainly want programs to be read by people and people prefer to read things once in a single pass.

In any respectable branch of engineering, failure to observe such elementary precautions would have long been against the law.

In effect, we conjure the spirits of the computer with our spells. (p. 1)

Computation provides a framework for dealing precisely with notions of “how to”. (p. xvi)

The user should not need to know how the procedure is implemented in order to use it. (p. 25)

Thus, programs must be written for people to read, and only incidentally for machines to execute. (p. xv)

“computer science” is not a science and that its significance has little to do with computers. (p. xvi)

you must read and write computer programs—many of them. It doesn’t matter much what the programs are about or what applications they serve. (p. xi)

They should feel secure about modifying a program, retaining the spirit and style of the original author. (p. xvi)

[A master software engineer] can visualize the behavior of his system in advance. (p. 2)

Protocols: Describe how an known action is taken on a Type.

Behaviors: Describe how a Type takes an known action.