Art, Decoration, Design
This is merely an attempt.
We often use these terms interchangeably, but here’s another crack at the distinction drawn between art, decoration, and design. On a Venn diagram, these 3 circles may overlap, but they are not congruent.
Art provokes, decoration adds*, and design solves.
This requires an examination of the intention and the effect. Any of these things could be visually pleasing or messy or referential or affiliative to a particular group. But none of those things are a requirement. But if a visual thing doesn’t provoke, adorn, or solve, it may not be very good.
Example: A hotel painting. Is it art? Probably not. Not if it doesn’t provoke anything (except maybe dread or malaise). Does it fill a wall in the interest of some kind of aesthetic? Sure, so it’s probably decoration. Was it put there to answer a need to add calmness and sense of inoffensive homeyness? Yeah, so there’s an argument to be made that it’s design.
Not everything has to be art.
*this is to say, decoration is not a thing in itself, like an art object or design object.