The Golden Mean
Our views on constitutes good composition has varied from one era to the next and from culture to culture. In
the Western world, much of our ideas about composition comes to us from classical Greece.  The Greeks looked
out at the natural world around them and noted the pervasiveness of certain proportions and relationships. One
of these is referred to as the Golden Mean or Golden Ratio. In Renaissance Italy, it was referred to as the “Divine
Proportion”.
Expressed as a formula, the Golden Mean appears like this:
B/A = C/B
In words, the smaller piece bears the same proportion to the larger piece, as the
larger piece bears to the whole. While this might seem a little esoteric, the Greeks
felt they could see this relationship all around them, in the branches of trees,
shell formations, and in the human body (e.g., arm is to leg as leg is to whole
body).
Next
architecture (window is to door as door is to wall, for instance).  The concept is so embedded in our culture, that
it is inherent in our evaluation of what constitutes a satisfying proportion.