On the way home, I was thinking about the overlap of engineering and design. Most engineering disciplines involve some element of design, but design and engineering are not the same thing. Similarly, some designers (particularly those working on Web site design and user interfaces) have begun to apply scientific and statistical principles to their work in a way that is very similar to how engineers work. That led me to come up with the following definition of engineering:

Engineering is the practice (or profession) of applying scientific principles, statistics, and standard materials or components to solve design problems subject to resource constraints.

The designer is the person who sketches out a bizarre Frank Gehry-style shape; the engineer is the person who uses knowledge of physics and the properties of standardized construction materials to specify the foundation and support structures required to keep it standing after the first blizzard or hurricane (but not necessarily any conceivable blizzard or hurricane) while remaining within the client’s budget.

I think the bit about constrained resources is particularly important and often overlooked. The nature of those constraints is different from one discipline to the next: for a software engineer, it may be time-to-market, memory consumption, or the necessity of processing a 4k-by-4k frame of video 30 times a second; for a civil engineer, the constraints may be geotechnical (will the soil support a bridge pier in this location?) or materials availability (can we physically get a precast box girder of the required size to this location?) or safety (what magnitude of earthquake must this containment building be able to withstand?). For an electrical engineer, the constraint may be component selection: how do I build this device in the same FPGA technology as we’re already using for some other high-volume product? For all engineering disciplines, cost is a constraint, and engineers are often called upon to optimize the trade-off between labor cost and materials cost, or between capital and operating (or manufacturing) expenses.

Having done that, I should perhaps compare what the experts who edit dictionaries have to say. The OED (my usual go-to reference since MIT has a subscription):

The branch of science and technology concerned with the development and modification of engines (in various senses), machines, structures, or other complicated systems and processes using specialized knowledge or skills, typically for public or commercial use; the profession of an engineer. Freq. with distinguishing word.

This gets most of the way there, but is a bit unsatisfying for a definition last revised in 2010. I think AHD’s definition (copyright 1992) is more to the point:

1.a. The application of scientific and mathematical principles to practical ends such as the design, manufacture, and operation of efficient and economical structures, machines, processes, and systems.

Note their mention of “efficient and economical”, which starts to capture the sort of resource constraints I think are relevant. Merriam-Webster provides two distinct definitions at m-w.com, which each capture different aspects of the profession. First:

the work of designing and creating large structures (such as roads and bridges) or new products or systems by using scientific methods

Second (“full definition”):

a : the application of science and mathematics by which the properties of matter and the sources of energy in nature are made useful to people
b : the design and manufacture of complex products

(There’s also a “Concise Encyclopedia” entry which is much too long to quote here.)

What do you think? Engineers, do any of these definitions adequately capture what your profession is about?