theory

explanatory, legislation, intuitively
explanatory：knowing the reasons why choose to design this shape
legislation：following the basic rule, make the work more efficient
Intuitively: cannot base every work on theory, but also cannot give up theory

Theory of design can help design, but it does not always precede design. A great idea with skill is more important

Source:http://www2.uiah.fi/projekti/metodi/135.htm