Edsger Dijkstra Quotes

I don't need to waste my time with a computer just because I am a computer scientist.

The computing scientist's main challenge is not to get confused by the complexities of his own making.

Yes, I share your concern: how to program well -though a teachable topic- is hardly taught. The situation is similar to that in mathematics, where the explicit curriculum is confined to mathematical results; how to do mathematics is something the student must absorb by osmosis, so to speak. One reason for preferring symbol-manipulating, calculating arguments is that their design is much better teachable than the design of verbal/pictorial arguments. Large-scale introduction of courses on such calculational methodology, however, would encounter unsurmoutable political problems.

It is a mistake to think that programmers wares are programs. Programmers have to produce trustworthy solutions and present it in the form of cogent arguments. Programs source code is just the accompanying material to which these arguments are to be applied to.

If debugging is the process of removing software bugs, then programming must be the process of putting them in.

There should be no such thing as boring mathematics.

The competent programmer is fully aware of the limited size of his own skull. He therefore approaches his task with full humility, and avoids clever tricks like the plague.

The question of whether computers can think is like the question of whether submarines can swim.

Why has elegance found so little following? That is the reality of it. Elegance has the disadvantage, if that's what it is, that hard work is needed to achieve it and a good education to appreciate it.

So-called "natural language" is wonderful for the purposes it was created for, such as to be rude in, to tell jokes in, to cheat or to make love in (and Theorists of Literary Criticism can even be content-free in it), but it is hopelessly inadequate when we have to deal unambiguously with situations of great intricacy, situations which unavoidably arise in such activities as legislation, arbitration, mathematics or programming.

Aim for brevity while avoiding jargon.

Write a paper promising salvation, make it a structured something or a virtual something, or abstract, distributed or higher-order or applicative and you can almost be certain of having started a new cult.

Some consider the puzzles that are created by their omissions as spicy challenges, without which their texts would be boring; others shun clarity lest their work is considered trivial.

The required techniques of effective reasoning are pretty formal, but as long as programming is done by people that don't master them, the software crisis will remain with us and will be considered an incurable disease. And you know what incurable diseases do: they invite the quacks and charlatans in, who in this case take the form of Software Engineering gurus.

Elegance is not a dispensable luxury but a factor that decides between success and failure.

... what society overwhelmingly asks for is snake oil. Of course, the snake oil has the most impressive names - otherwise you would be selling nothing - like "Structured Analysis and Design", "Software Engineering", "Maturity Models", "Management Information Systems", "Integrated Project Support Environments" "Object Orientation" and "Business Process Re-engineering".

Thanks to the greatly improved possibility of communication, we overrate its importance. Even stronger, we underrate the importance of isolation.

Much of the excitement we get out of our work is that we don't really know what we are doing.

Experience does by no means automatically leads to wisdom and understanding.

I mentioned the non-competitive spirit explicitly, because these days, excellence is a fashionable concept. But excellence is a competitive notion, and that is not what we are heading for: we are heading for perfection.

Our intellectual powers are rather geared to master static relations and that our powers to visualize processes evolving in time are relatively poorly developed. For that reason we should do (as wise programmers aware of our limitations) our utmost to shorten the conceptual gap between the static program and the dynamic process, to make the correspondence between the program (spread out in text space) and the process (spread out in time) as trivial as possible.

The traditional mathematician recognizes and appreciates mathematical elegance when he sees it. I propose to go one step further, and to consider elegance an essential ingredient of mathematics: if it is clumsy, it is not mathematics.

In the good old days physicists repeated each other's experiments, just to be sure. Today they stick to FORTRAN, so that they can share each other's programs, bugs included.

When we take the position that it is not only the programmer's responsibility to produce a correct program but also to demonstrate its correctness in a convincing manner, then the above remarks have a profound influence on the programmer's activity: the object he has to produce must be usefully structured.

Don't blame me for the fact that competent programming, as I view it as an intellectual possibility, will be too difficult for the average programmer, you must not fall into the trap of rejecting a surgical technique because it is beyond the capabilities of the barber in his shop around the corner.

The art of programming is the art of organizing complexity.

About the use of language: it is impossible to sharpen a pencil with a blunt axe. It is equally vain to try to do it with ten blunt axes instead.

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

The ability of discerning high quality unavoidably implies the ability of identifying shortcomings.

APL is a mistake, carried through to perfection. It is the language of the future for the programming techniques of the past: it creates a new generation of coding bums.

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

Don't compete with me: firstly, I have more experience, and secondly, I have chosen the weapons.

John von Neumann draws attention to what seemed to him a contrast. He remarked that for simple mechanisms, it is often easier to describe how they work than what they do, while for more complicated mechanisms, it is usually the other way around.

[Though computer science is a fairly new discipline, it is predominantly based on the Cartesian world view. As Edsgar W. Dijkstra has pointed out] A scientific discipline emerges with the - usually rather slow! - discovery of which aspects can be meaningfully 'studied in isolation for the sake of their own consistency.

Please don't fall into the trap of believing that I am terribly dogmatical about [the goto statement]. I have the uncomfortable feeling that others are making a religion out of it, as if the conceptual problems of programming could be solved by a single trick, by a simple form of coding discipline!

The students that, like the wild animal being prepared for its tricks in the circus called 'life', expects only training as sketched above, will be severely disappointed: by his standards he will learn next to nothing.

If we wish to count lines of code, we should not regard them as 'lines produced' but as 'lines spent.'

I think of the company advertising "Thought Processors" or the college pretending that learning BASIC suffices or at least helps, whereas the teaching of BASIC should be rated as a criminal offence: it mutilates the mind beyond recovery.

If you want more effective programmers, you will discover that they should not waste their time debugging, they should not introduce the bugs to start with.

We are all shaped by the tools we use, in particular: the formalisms we use shape our thinking habits, for better or for worse, and that means that we have to be very careful in the choice of what we learn and teach, for unlearning is not really possible.

In this respect a program is like a poem: you cannot write a poem without writing it. Yet people talk about programming as if it were a production process and measure "programmer productivity" in terms of "number of lines of code produced". In so doing they book that number on the wrong side of the ledger: we should always refer to "the number of lines of code spent".

When I came back from Munich, it was September, and I was Professor of Mathematics at the Eindhoven University of Technology. Later I learned that I had been the Department's third choice, after two numerical analysts had turned the invitation down; the decision to invite me had not been an easy one, on the one hand because I had not really studied mathematics, and on the other hand because of my sandals, my beard and my "arrogance" (whatever that may be).

I would therefore like to posit that computing's central challenge, how not to make a mess of it, has not yet been met.

When we had no computers, we had no programming problem either. When we had a few computers, we had a mild programming problem. Confronted with machines a million times as powerful, we are faced with a gigantic programming problem.

Mathematicians are like managers - they want improvement without change.

Brainpower is by far our scarcest resource.

In their capacity as a tool, computers will be but a ripple on the surface of our culture. In their capacity as intellectual challenge, they are without precedent in the cultural history of mankind.

There is very little point in trying to urge the world to mend its ways as long as that world is still convinced that its ways are perfectly adequate.

We must be very careful when we give advice to younger people: sometimes they follow it!

As a slow-witted human being I have a very small head and I had better learn to live with it and to respect my limitations and give them full credit, rather than to try to ignore them, for the latter vain effort will be punished by failure.

The prisoner falls in love with his chains.

Teaching to unsuspecting youngsters the effective use of formal methods is one of the joys of life because it is so extremely rewarding.

The lurking suspicion that something could be simplified is the world's richest source of rewarding challenges.

If there is one 'scientific' discovery I am proud of, it is the discovery of the habit of writing without publication in mind.

FORTRAN, the infantile disorder, by now nearly 20 years old, is hopelessly inadequate for whatever computer application you have in mind today: it is now too clumsy, too risky, and too expensive to use.

The use of anthropomorphic terminology forces you linguistically to adopt an operational view. And it makes it practically impossible to argue about programs independently of their being executed.

Thank goodness we don't have only serious problems, but ridiculous ones as well.

The effort of using machines to mimic the human mind has always struck me as rather silly. I would rather use them to mimic something better.

Beauty is our business.

Production speed is severely slowed down if one works with half-time people who have other obligations as well. This is at least a factor of four; probably it is worse.