Definition: Greatness is that on account of which goodness, eternity or duration etc. are great, and it encompasses all extremes of every being that has the greatness required for its own perfection.
Clarification: Greatness is considered in the Art not merely as quantity or physical dimension, but chiefly as magnificence. And greatness is the prime diffusing entity through final, efficient, formal and material causes where the final cause has greater magnitude than the efficient cause and the efficient cause than the formal cause and form than matter. And the same applies to the accidents of substantial beings. However, greatness must be considered as a unique principle on its own.
Distinctions: There are many magnitudes, all distinct in essence and nature, some greater than others, some equal to others, in different ways all the way up to supreme magnitude or the ultimate principle of all other magnitudes that simply exists as one great being under whose orderly rule all other magnitudes of great things appear as likenesses and images where the human intellect reflects on supreme magnitude. In lower magnitudes the intellect apprehends higher magnitude as an intense form, as it were infinite without quantity in the figure of cosmic extension - if there really is such a form - representing supreme magnitude.
Conditions: We showed above that without greatness there is no final cause perfecting the efficient, formal and material causes; now, final perfection depends on greatness given that a being not perfect in its own way cannot be great.
Nature: The essence of greatness fully consists in its intrinsic correlatives: the magnifier, magnified and magnification are one intrinsic essence of greatness.