I think it all comes down to relationships.
Art is different from ordinary reality. It is a reality of its own. It is like an altered state. And the nature of its meaning (the meaning which we personally experience and the quality of our experience) has something to do not only with the nature of the elements themselves that define what may appear to be a discreet "work of art," but with the nature of relationships that are happening on numerous levels. And it is these relationships that equally define the work.
There is the nature of elements that make up a work. Line, form, color, size, etc. There are relationships between the formal elements themselves that may define a discreet object. Color relationships, tonal relationships, size and position relationships. There is the nature of the context/surroundings in which a work is experienced, and there is the relationship between the work and this presentation context. Formal relationships, informational relationships, implicit and explicit. In fact, the work of art cannot be separated from the surrounding elements within which it is experienced. There is the relationship to a viewer (physical, personal, cultural), the relationship to ordinary reality, and the relationship to the nature of human experience on the deepest level. Meaning is contextual (as when blue appears a certain way because it is next to yellow), but meaning conveyed by forms often has to do with the shared context of what it is to experience life as a human in this world (such as up versus down, standing versus repose, and relative size).
An artist can manipulate the relationships to provide a particular experience, help us to see things in a different way, or alter our consciousness about something. It is often an aesthetic, intuitional mindset that guides an artist's decisions about defining and working with the elements of the medium.
To try and understand what puts something in the realm of Art, I think of a pair of scissors. Granted, a scissors can be beautiful. It can afford an aesthetic experience. And, we can look at it with an aesthetic artistic mindset as if we were looking at a work of art on display somewhere. But I simply ask: were there aesthetic considerations? Was there intention on any level to create art? Does something about its nature alter our consciousness in any way about anything including the scissors themselves?
One of my favorite quotes is from an art scholar from the 1960's,
Philip Larsen: Art has "...the potential to excite sensations not often possible in the ordinary world. If it does nothing but that, we should be grateful."