Space and form can be perceived as an additive or subtractive composition.

An additive composition is one in which pieces appear to have been combined together to create the whole, much like pieces of clay added on to one another.

A subtractive composition is one in which bits appear to have been chipped away from a monolithic block, much like a sculptor chips away pieces until the final sculpture is visible. The eye fills in missing parts to see a whole solid as the unity of composition.