Final answer:
The Greek definition of symmetry according to Vitruvius is proportional harmony, which emphasizes a balanced composition, achieved through the golden ratio and ideal geometric forms.
Step-by-step explanation:
The Greek definition of "symmetry" as transmitted by Vitruvius is b. Proportional harmony. This concept of symmetry is not just about geometric precision or merely mirroring one side to another but is deeply rooted in the sense of proportion and balance. This idea is evident in classic Greek architecture and sculpture which often relies on the use of the golden ratio to create a sense of perfect balance and harmony that is inherently pleasing to the human eye.
Examples in art include the use of bilateral symmetry, which we can see in Perugino's painting, creating a sense of stability and formality. Symmetry in Greek art and architecture is also associated with mathematical precision as seen in the construction of the Parthenon, which embodies the golden ratio. The essence of Greek symmetry is about achieving a balanced composition with ideal geometric forms as a reflection of beauty and perfection.