It could be constrained by forces of nature or analytical techniques to describe nature.   It could be controlled by local construction methods, material availability, or an engineer's own ingenuity.   A design can be borne by art and uncertainty as much as it can be borne by science and certainty.   Anyone who doesn't know this is not an engineer.  Isler created the thin concrete shell, a pillowcase shape, when he viewed burlap hanging over rebar.  The artist Kenneth Snelson developed the tensegrity by playing with sticks and strings.   The artist, Ai WeiWei created the bird's nest form used for the Beijing National Stadium for the 2008 Olympics by looking at one.  Bucky Fuller created the geodesic dome through sculpture and play.   He fooled around with stuff like triangles made out of spaghetti, not math.   The inventor Theo Jansen is the master of amazingly lifelike kinetic sculptures without math or science.  Math and science rarely contribute to the creation of the design (there are very few exceptions).    So why are we engineers not making stuff in school?   Who knows!