The structural unity of the parts is such that, if any one of them is displaced or removed, the whole will be disjointed and disturbed. For a thing whose presence or absence makes no visible difference is not an organic part of the whole.
Moller, in his Essay on Architecture, taught that the building which was fitted accurately to answer its end would turn out to be beautiful, though beauty had not been intended. I find the like unity in human structures rather virulent and pervasive.
Unity of command is essential to the economy of time. Warfare in the field was like a siege: by directing all one's force to a single point a breach might be made, and the equilibrium of opposition destroyed.
The unity of effect or impression is a point of the greatest importance. It is clear, moreover, that this unity cannot be thoroughly preserved in productions whose perusal cannot be completed at one sitting.