Unity means that all the parts fit together. In music, we designate a piece for a key such as Beethoven's Violin Concerto in D Major. The title of the piece suggests that whatever goes on in the violin concerto fits somehow with the key of D. It might fit by contrast or by similarity. The same principle works in visual art--parts all need to belong either by contrast or by similarity.
The opposite of unity is fragmentation. In life and in art, to fragment is to fall apart, to break away from the whole, and the result is incompleteness. So how do we know if our painting is fragmenting and what can we do about it? Here is where I would like very much to do the unkind thing and show some examples of fragmented art, but it would be best to try to use another approach. Let's try explaining:
Generally an art work will not fragment if it has...
- a strong connecting pattern of darks and lights that hold it together
- a good balance so that we don't feel one-sidedness
- a visual path to avoid aimlessness
Look at how the lights connect to other lights and darks connect to other darks. Let's throw it into a notan so you can see this better. That's what we mean by point number 1Staying with Sargent, let's look for balance in point number 2. The strong vertical of the waterfalls and two figures is counter-balanced by the horizontal ornate rail in the background as well as the horzontal surface on which the woman is sitting. Nothing feels topsy-turvy.
And what about point number 3? A good visual path is as necessary to unity as a plot is to a novel. Without it, the eye just doesn't know where to go. Look at this wonderful path created by Sargent. Arguably other organizing methods can help prevent fragmentation, but I contend that if these three are working, the chances are better than average that the piece will have unity. And I believe that when a work has unity, it will stand the test of time.