We can’t exhaustively define God, of course, but this description cited by Dallas Willard is edifying.
God is “the eternal, independent, and self-existent Being; the Being whose purposes and actions spring from Himself, without foreign motive or influence; he who is absolute in dominion; the most pure, the most simple, the most spiritual of all essences; infinitely perfect; and eternally self-sufficient, needing nothing that he has made; illimitable in his immensity, inconceivable in his mode of existence, and indescribable in his essence; known fully only by himself, because an infinite mind can only be fully comprehended by itself. In a word, a Being who, from his infinite wisdom, cannot err or be deceived, and from his infinite goodness, can do nothing but what is eternally just, and right, and kind.”
— Adam Clarke in Cyclopaedia, vol. 3 (New York: Harper & Brothers, 1894), 903-4, quoted by Dallas Willard in Knowing Christ Today, chapter 4, n. 1.
“Metaphysical objects that are not actualized somewhere in space and time, that is, non-particulars such as numbers, properties, relations, propositions, and classes. They stand in contrast to spatio-temporal physical objects.
“Whether these entities actually exist—whether we should ascribe reality to them—is a question of persistent dispute in philosophy. Empiricists and nominalists try to conceive of abstract entities as having merely a linguistic basis. However, if mathematics embodies general truths about the world and has abstract entities as its subject matter, abstract entities would be objects of reference and hence real existents. This is the claim of Platonism and is also a position admitted by Quine’s criterion of ontological commitment. The discussion of abstract entities is related to problems of being, to the problem of universals, also to the theory of meaning.”
— The Blackwell Dictionary of Western Philosophy (Wiley, 2009), 4.
“St. Augustine (C.E. 354-430), originally named Aurelius Augustinus, was the Catholic bishop of Hippo in northern Africa. He was a skilled Roman-trained rhetorician, a prolific writer (who produced more than 110 works over a 30-year period), and by wide acclamation, the first Christian philosopher. Writing from a unique background and vantage point as a keen observer of society before the fall of the Roman Empire, Augustine’s views on political and social philosophy constitute an important intellectual bridge between late antiquity and the emerging medieval world. Because of the scope and quantity of his work, many scholars consider him to have been the most influential Western philosopher.
“Although Augustine certainly would not have thought of himself as a political or social philosopher per se, the record of his thoughts on such themes as the nature of human society, justice, the nature and role of the state, the relationship between church and state, just and unjust war, and peace all have played their part in the shaping of Western civilization. There is much in his work that anticipates major themes in the writings of moderns like Machiavelli, Luther, Calvin and, in particular, Hobbes.” (continue article)
—J. Mark Mattox at The Internet Encyclopedia of Philosophy
“An early theoretical use of the concept occurs in Malebranche [Treatise on Nature and Grace] 1674, I, §13; [Dialogues on metaphysics] 1688, 2, 3: Our world is one among the many possible worlds that God could have created. This world, which he did create, differs from the others by the greater simplicity of its laws. The concept is also important in Leibniz’s philosophy. In the Theodicy 1710 he argues that our actual world, having been created by God, a being with all perfections, is the best of all the worlds that he might have created, i.e., the best possible world.
“When explaining the modal concepts of possibility, contingency and necessity, the following pattern of explanation, originating with Leibniz, has proved to be very attractive: A proposition p is necessary if p is true in all possible worlds; a proposition p is possible if p is true in some possible world. The advantage of this pattern of analysis is that the relations between modal concepts are, in a sense, reduced to the relations between the concepts of ‘all’ and ‘some,’ which are accounted for in modern predicate logic.
“Many contemporary philosophers and logicians find the idiom of possible worlds convenient but regard it as a figurative mode of expression only, whilst others, among whom David Lewis is foremost, argue that there is a plurality of worlds.”
— The Penguin Dictionary of Philosophy, 482-483.