Henry Petroski Quotations

Science is about knowing; engineering is about doing.

An over-reliance on past successes is a sure blueprint for future failures.

As engineers, we were going to be in a position to change the world - not just study it.

Successful design is not the achievement of perfection but the minimization and accommodation of imperfection.

Successful engineering is all about understanding how things break or fail.

All conventional wisdom has an element of truth to it, but good design requires more than an element of truth - it requires an ensemble of correct assumptions and valid calculations.

We can't simply blame the engineers when things go wrong because, no matter how well they plan, things don't always go according to plan.

The same aspirations to celebrate and uplift the spirit that drove the Egyptians to build the pyramids are still driving us. The things we're doing differ only in magnitude.

It has been said, by engineers themselves, that given enough money, they can accomplish virtually anything: send men to the moon, dig a tunnel under the English Channel. There's no reason they couldn't likewise devise ways to protect infrastructure from the worst hurricanes, earthquakes and other calamities, natural and manmade.

Betting on the success of innovative technologies in the marketplace can carry all the uncertainty and risk that betting on the next card in the deck does at a blackjack table in Las Vegas. There is a factor of randomness that must be factored in, but precisely how to do so is anyone's guess.

It seems to be a law of design that for every advantage introduced through redesign, there is an accompanying unintended disadvantage.

Failure is Central to engineering. Every single calculation that an engineer makes is a failure calculation.

You can almost say that a design error is a human error because, after all, it's we humans who do the designing.

Any design, whether it's for a ship or an airplane, must be done in anticipation of potential failures.

Many of the familiar little things that we use every day have typically evolved over a period of time to a state of familiarity. They balance form and function, elegance and economy, success and failure in ways that are not only acceptable, but also admirable.

Too much redesign has to do more with fad and fashion than with fitness and function. It is change for the sake of change. Such redesign is not only unnecessary, it is all too often also retrogressive, leading to things that work less effectively than those they were designed to replace.

I was always told that I was good in mathematics, and I guess my grades and standardized test scores supported that. My worst subjects were those that generally involved a lot of reading - English and history. So, having good test scores in math and mediocre ones in reading, I was naturally advised to major in engineering in college.

The paradox is that when we model future designs on past successes, we are inviting failure down the line; when we take into account past failures and anticipate potential new ways in which failure can occur, we are more likely to produce successful designs.

Because they are so humbled by their creations, engineers are naturally conservative in their expectations of technology. They know that the perfect system is the stuff of science fiction, not of engineering fact, and so everything must be treated with respect.

Everything we do is designed, whether we're producing a magazine, a website, or a bridge. Design is really the creative invention that designs everything.

Relying on nothing but scientific knowledge to produce an engineering solution is to invite frustration at best and failure at worst.

Indeed, an engineer designing a structure is not unlike an artist painting one. Both start with nothing but talent, experience, and inspiration. The fresh piece of paper on the drawing board is as blank as the newly stretched piece of canvas.

I emphasize that virtually every engineering calculation is ultimately a failure calculation, because without a failure criterion against which to measure the calculated result, it is a meaningless number.

My first book, 'To Engineer Is Human,' was prompted by nonengineer friends asking me why so many technological accidents and failures were occurring. If engineers knew what they were doing, why did bridges and buildings fall down? It was a question that I had often asked myself, and I had no easy answer.

I employ case studies of failure into my courses, emphasizing that they teach us much more than studies of success. It is not that success stories cannot serve as models of good design or as exemplars of creative engineering. They can do that, but they cannot teach us how close to failure they are.

The definition of 'safe' is not strictly an engineering term; it's a societal term. Does it mean absolutely no loss of life? Does it mean absolutely no contamination with radiation? What exactly does 'safe' mean?

Luxury, not necessity, is the mother of invention. Every artifact is somewhat wanting in its function, and that is what drives its evolution.

No design, no matter how common or seemingly insignificant, is without its adamant critics as well as its ardent admirers.

Case studies of failure should be made a part of the vocabulary of every engineer so that he or she can recall or recite them when something in a new design or design process is suggestive of what went wrong in the case study.

I relax by looking at things and reading about things. Even the simplest thing can reveal a great deal about the world around us. It relaxes me greatly to sit back with my feet up and look around my study at the everyday things that surround me.

The space shuttle was designed, at least in part, to broaden our knowledge of the universe. To scientists, the vehicle was a tool; to engineers, it was their creation.

There's so much written about the Titanic, and it's hard to separate what's fact and what's fiction. My understanding is that the way the Titanic was designed, the emphasis was placed on surviving a head-on collision.

We call the fates of the Titanic and the Concordia - as well as those of the space shuttles Challenger and Columbia - 'accidents.' Foreseeing such undesirable events is what engineers are expected to do. However, design trade-offs leave technological systems open to failings once predicted, but later forgotten.

Typically, highway bridges have about 50 years. But over in England, they have iron bridges approaching 250 years. In France, there are Roman aqueducts that are approaching 2,000 years old. So a bridge can last a very long time if it's built properly in the first place and then maintained properly.

It is really want, rather than need, that drives the process of technological evolution.

Many new technologies come with a promise to change the world, but the world refuses to cooperate.

I'm a firm believer that no matter how small an object is, you can find interesting things out about it and its history.

If I could go upstairs and write every day, I would be happy. I don't need recreation.

Read and write with a sensitive ear. The craft of writing is very important. Practice the craft.

A common misconception about how things such as space shuttles come to be is that engineers simply apply the theories and equations of science. But this cannot be done until the new thing-to-be is conceived in the engineer's mind's eye. Rather than following from science, engineered things lead it.

Because every design must satisfy competing objectives, there necessarily has to be compromise among, if not the complete exclusion of, some of those objectives, in order to meet what are considered the more important of them.

Failures are much more dramatic than successes, and people like drama. I think this is why automobile races draw such crowds. People expect spectacular crashes, which we tend to find more interesting than cars just racing around the track. The same is true of bridges, buildings, or any structure or machine.

Although engineers want always to make everything better, they cannot make anything perfect. This basic characteristic flaw of the products of the profession's practitioners is what drives change and makes achievement a process rather than simply a goal.

As long as there are things to wonder about, there are stories to be written about them. That makes me happy, because writing about things seems to be my thing.

Companies selling a product play down its vulnerability and emphasize its robustness. But only after technology leaves the dock is it really tested. For human operators in control of a supposedly infallible system, complacency and overconfidence can take over, and caution may be thrown to the wind.

For as long as I can remember, I have been fascinated by things large and small. I wanted to know what made my watch tick, my radio play, and my house stand. I wanted to know who invented the bottle cap and who designed the bridge. I guess from early on I wanted to be an engineer.

I have always been fascinated by the way things work and how they came to take the form that they did. Writing about these things satisfies my curiosity about the made world while at the same time giving me an opportunity to design a new explanation for the processes that shape it.

The Book of the Heart provides a fresh perspective on the influence of the book as artifact on our language and culture. Reading this book broadens our appreciation of the relationship between things and ideas.

Any design, whether its for a ship or an airplane, must be done in anticipation of potential failures.

Our expectations for a technology rise with its advancement.

Form follows failure.

Whether or not science can be applied to that mental construct [i.e. the designed entity] is a matter of availability. If there is body of scientific knowledge that can be applied, then it would be foolish not to exploit it. However, if there is none, it does not mean that the thing cannot be designed, made, and used safely.

Design is nothing if not decision making.

What is commonly overlooked in using the computer is the fact that the central goal of design is still to obviate failure, and thus it is critical to identify exactly how a structure may fail. The computer cannot do this by itself . . .

A failed structure provides a counterexample to a hypothesis and shows us incontrovertibly what cannot be done, while a structure that stands without incident often conceals whatever lessons or caveats it might hold for the next generation of engineers.

The plain wooden toothpick, it may be argued, is among the simplest of manufactured things. It consists of a single part, made of a single material, intended for a single purpose-from which it gets its simple name. It is also among the most convenient and ready of things. It can be used directly out of the box-there being no instructions to read, no parts to assemble, no priming or booting required, and no maintenance expected. When it has served its purpose, it is simply discarded.

The bookshelf, like the book, has become an integral part of civilization as we know it, its presence in a home practically defining what it means to be civilized, educated, and refined.

Engineering is achieving function while avoiding failure.

Engineering, like poetry, is an attempt to approach perfection. And engineers, like poets, are seldom completely satisfied with their creations. They notice, even if no one else does, the world that is not quite le mot juste, or the hairline crack that blemishes the structure.

No one wants to learn from mistakes, but we cannot learn enough from successes to go beyond the state of the art.

The most amazing achievement of the computer software industry is its continuing cancellation of the steady and staggering gains made by the computer hardware industry.

Engineers are not superhuman. They make mistakes in their assumptions, in their calculations, in their conclusions. That they make mistakes is forgivable; that they catch them is imperative. Thus it is the essence of modern engineering not only to be able to check one's own work but also to have one's work checked and to be able to check the work of others.