American Scientist

The practice of engineering, like that of science, necessarily involves making assumptions, drawing inferences and framing hypotheses. These mental constructs represent cognitive choices that often must be made among mutually exclusive ideas. If an engineer is asked to design a bridge, the informed choice may be between a suspension and a cable-stayed type. For the sake of analysis, one of these will be assumed and the other all but forgotten. The analysis, which itself involves numerous choices among details large and small, results in a design and a cost for that design. The alternative bridge type can later be assumed and analyzed to completion, providing the basis for comparison on functional, aesthetic and economic grounds. A final choice among all the hypothetical bridges results in the bridge that is built.