[dkarl]

Everything Dijkstra says makes sense if you believe that computing cannot scale without correctness. He was wrong about that one thing, and to be fair to him, it's still a little amazing in retrospect, even when we can look back over the decades of history through which we've created a society dependent on vast, unimaginably complex, world-spanning computing systems built out of pieces that are virtually all broken.

And it's not like he was a lone crank railing against the 99% who were moving forward with a well-founded idea of how computing could scale indefinitely by composing incorrect programs. Just like today, 99% of programming, including programming for government programs and vital infrastructure, was done by people who were only hoping to make their own projects succeed well enough for the next six months to three years. I'm sure there were brilliant people who made intelligent arguments against the need for correctness, but their arguments didn't carry the day. Complacency and short-term thinking did.

In that context, Dijkstra's pessimism and his use of harsh, attention-getting language makes a lot of sense. How many people at the time really understood that in 2020 every part of our civilization would depend on code compiled by compilers with bugs, linked with libraries with bugs, in virtual machines with bugs, on operating systems with bugs, on CPUs with bugs in their microcode, and yet it would still all mostly work?

[munificent]

> if you believe that computing cannot scale without correctness. He was wrong about that one thing, and to be fair to him, it's still a little amazing in retrospect,

That is clearly wrong if one is willing to take a moment to stop gazing at the wonder of pure mathematics and look at the outside world. There is no notion of "correctness" for the pyramids of Egypt, the dykes of the Netherlands, Milan Cathedral, or the world economy and yet those huge-scale systems all function.

> Dijkstra's pessimism and his use of harsh, attention-getting language makes a lot of sense.

It makes sense in terms of Dijkstra's personality, but it makes no logical sense. If you believe mathematical correctness is such a valuable principle, then you should be able to leverage that same principle in one's own arguments. The fact that Dijkstra couldn't dispassionately prove that correctness was vital and had to resort to emotionally-loaded weasel words undermines his own claim.

[ThenAsNow]

> That is clearly wrong if one is willing to take a moment to stop gazing at the wonder of pure mathematics and look at the outside world. There is no notion of "correctness" for the pyramids of Egypt, the dykes of the Netherlands, Milan Cathedral, or the world economy and yet those huge-scale systems all function.

Wow, couldn't disagree with this more, at least on your examples of civil engineering (buildings, dikes). There are testable, comprehensive physical principles that govern whether any of these engineered products function in their most fundamentally-intended ways. This is the reason most buildings are resilient and don't collapse under load, or that dams keep water from flowing uncontrolled. You can debate "correctness" in the sense of the purpose the product serves, but there is the principle of correctness of construction which your civil engineering examples (and anything truly engineered) satisfy. Correctness in construction is not subjective.

[raiph]

> Correctness in construction is not subjective.

Perhaps, but it's never certain. So things that are "correct" can still be wrong.

Here's how Einstein expressed his disagreement with what you are saying:

> As far as the laws of mathematics are certain, they do not refer to reality, and as far as they refer to reality, they are not certain.

Nothing in physics (or any other science) is certain. All one can do in science (other than mathematics) is disprove. One cannot prove.

To prove you would have to be all knowing. You would have to have taken into account all relevant aspects of all physical characteristics. For example, all known aspects of quantum mechanics, including the uncertainty principle, AND all relevant unknown aspects of quantum mechanics, which is guaranteed to be hit and miss, and can rationally be expected to contain an unknown number of misses that isn't zero.

It's the human propensity to ignore these fundamentals that leads to things like the Tacoma Bridge collapse.[0]

[0] https://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge_(1940)

[munificent]

> There are testable, comprehensive physical principles that govern whether any of these engineered products function in their most fundamentally-intended ways.

These are statistical engineering tests of the probability of failure under certain conditions. That is not at all what Dijkstra would consider to be "correctness". Dijkstra is talking about mathematical proof. In mathematics, one does not say "1 + 2 = 3 plus or minus 0.1 with a safety factor of 2".

[ThenAsNow]

When we determine if an aircraft trims, or a boat floats, it is not correct to say it is statistical engineering test of the probability of failure. You formalize the properties the system must have in order to not fail, and you use conservation equations to ultimately compute whether or not the system satisfies those properties. Margins are used to account for parameters that have uncertainty attached. All of these elements are subject to symbolic mathematical formalism. One can quite clearly state the inequalities that must be satisfied to be, e.g., controllable.

It's unclear how this would be any different than mathematically formalizing a distributed system, identifying the properties that constitute correctness of operation of that distributed system, and symbolically proving that subject to certain assumptions, the distributed system model does or does not satisfy those properties. This would presumably be consistent with the Dijkstra view of mathematical correctness.

[dkarl]

> There is no notion of "correctness" for the pyramids of Egypt, the dykes of the Netherlands, Milan Cathedral, or the world economy and yet those huge-scale systems all function.

I think it's impossible to come up with a rational judgment of whether the world economy "functions." I mean, those of us who are alive are alive, but there are a lot of things that have happened that haven't been ideal.

Besides the world economy, nothing you mention has the functional complexity of a large piece of software, and none of it was designed and built with much confidence, other than confidence that came from similarity to previous designs, and from an optimistic outlook that issues encountered during construction could be coped with. This wall is cracking, so we tear it down and rebuild it a little thicker. We have a few centuries, after all. I think you're right that modern software projects are analogous to ancient pyramids and medieval cathedrals. That's pretty much where we are. Yet somehow, working at that low level of sophistication, we've built working software that is orders of magnitude more complex than cathedrals.

I'm not saying I know how to improve on the situation, or even that we can; I'm just pointing out how different it is from, say, contemporary structural engineering where we can analyze the design of a novel structure and have a pretty good idea of whether it will be safe based on its geometry and known characteristics of materials and how they're joined. It's amazing that we've reached the scale we have with nothing comparable.

> If you believe mathematical correctness is such a valuable principle, then you should be able to leverage that same principle in one's own arguments.

The idea that mathematical reasoning is on some spectrum with dispassionate discourse has motivated hundreds of years of attempts to improve natural language by making it more mathematical. Result: some interesting contributions to philosophy but very little change in how people communicate. People are still people.

[watwut]

Imo, the real issue is that people seem to think that smart mathematicians or scientists don't argue like normal people, don't get emotional when arguing and always talk from divine truth.

The issue have nothing to do with mathematical correctness, so you can't apply the same principles. This is not math. But, Dijkstra's it's not being logical in arguments, because he is not of dick and likely this style of arguing was working for him in his life.

[galaxyLogic]

Good points. I think a way of looking at it is that much of software development we do today is about communication, not engineering. Think of web-sites they are all about communicating something. And in a sense when you write a program you do so to communicate with the computer.

Of course there are critical software engineering projects as well, Boeing MAX comes to mind.