Humans seem to be born with an innate sense of balance. We seek out balance in our everyday lives--it is comfortable. Balance has to do with the distribution of visual weight within a composition. This definition makes the concept seem rather complicated, but even small children have the ability of knowing when something is balanced or unbalanced.
As we observe the world around us we subconsciously assign vertical axis and expect to see an equal distribution on either side of them. Take for example, the shelving in my apartment (shown in the two photographs above). I am willing to bet that within the first glance you have already assigned a vertical axis to the composition--and you did it with out even knowing that that is what you were in fact doing. Am I right? Just to be sure we are on the same page, the vertical axis runs through the end of the top shelf and the beginning of the second shelf. It is on either side of this "line" that we are expecting to see a visual equilibrium.
To make the shelving a visually pleasing part of this interior space it needs to be balanced. Seeing as the items going on either side of the axis are not identical we aren't looking for symmetrical balance (a balance in which one side becomes the mirror image of the other side). Instead, we are looking for an asymmetrical balance. This is when balance is achieved with dissimilar objects that have equal eye attraction or visual weight.
In the first photo we are left rather uneasy and dissatisfied. This is due to the uneven visual weight either side of the vertical axis. On the left of the axis there are two large items and one small item. On the right of the axis there is only one large item and two small items. The shelving is clearly unbalanced.
In the second photograph I balanced the shelving composition by placing a large item, a mirror, on the right shelf, and thus on the right of the axis. Now the left side of the axis contains two large items and two small items. The right side of the axis has one large, one extra large, and one small item. The extra large item makes up for the lack of a second small item.
Visually, both sides of the vertical axis weigh the same. Neither side of the axis demands more attention from the viewer's eye, neither does one shelf look incomplete compared to the other. The shelving composition is balanced, and the viewer innate search is achieved.
