The essence of design is solving problems in elegant ways. Thus, we use the word "design" in multiple contexts, from what seems to be rote engineering to what appears to be mere decoration. In either case, and anything in between, we're "designing" if we're solving a problem.
Essence of Aesthetics from Art
The laws of aesthetics, however, come from art. As Paul Rand writes, "Without aesthetics, talk about art is not about art." If we want to know about how appearances and form affect content, the discourse is alive and well in art criticism.
But aesthetics is a curious field. It's principles are applicable to the visual design of digital products and websites, the presentation of data visualizations, even the treatments of architecture, but aesthetics garners admiration and misunderstanding more than any other aspect of creation. Its value is unparalleled in fields like fashion and automotive design but is dismissed as near worthless in other more technical industries.
Design and Appearances
As designers are fond of invoking, Steve Jobs once famously said,
Most people make the mistake of thinking design is what it looks like. People think it's this veneer – that the designers are handed this box and told, "Make it look good!" That's not what we think design is. It's not just what it looks like and feels like. Design is how it works.
But how something looks can affect how it works. That's why we italicize and embolden text; we achieve emphasis by changing the appearance of words. The fact that the italic text is aesthetically pleasing doesn't make it less less valuable; if the italic solves the problem of making the text more emphatic and distinct, then this aesthetic move has achieved the design goal, and it is consequently well designed.
Design may not be about making something pretty, but if the design is pretty, that doesn't mean it doesn't work, nor does it mean the aesthetics are frivolous or time was wasted. The most elegant designs solve multiple problems with as few elements as possible, and aesthetic treatments can do that just as any other design move can.