Remember the drill? Which of these things does not belong?

Example #1 (apple, banana, carrot). Easy! A carrot isn’t a fruit, so it doesn’t belong.

Example # 2 (cat, dog, butterfly). Well, a butterfly isn’t a mammal, so it doesn’t belong.

The logical point in each example is that the first two items belong to the same genus but they differ in species, that is, they have a specific difference. In contrast, the third item belongs to an altogether different genus.

Got it? Ready for another example?

Example #3 (Zeus, Wodan, God). Still easy. God isn’t a mythical deity, whether in Greek or Germanic mythology. So God doesn’t belong with Zeus and Wodan. Even a Unitarian, who believes in at most one God, would agree.

Well, then, in what genus does God belong? None.

But wait! Doesn’t God belong to the genus of existing entities, along with cat, dog, butterfly, and zillions of other things—each distinguished with respect to a specific difference? No, because God alone is identical with his existence. Everything else happens to exist but need not. Indeed, God, who exists necessarily, is the sustaining cause of everything that happens to exist. God doesn’t draw a specific form of existing from that which determines membership in genus. Nor does God  have some specific difference distinct from being, since only non-being, that is, nothing, is other than being. God isn’t a species within some genus. That all this invites sober reflection calls to mind the ancient imperative “Hear, O Israel, the Lord thy God is One.”

Recently a group of friends with whom my wife and I regularly pray discussed whether in the liturgy we join our prayers with the prayers offered to God by all people of all religions. The answer is “it depends.” Where is it that the people of a given religion locate God? If upon consideration they locate God in a genus, if they duly assign to God some specific difference, then it seems that they have badly misplaced God. To be sure, such a people, in the economy of salvation and with amazing grace, might someday come to worship God. Through our fault, we might someday fail to worship God. But for now we do not worship the same, indeed, the one and only, God. To make this claim is not faint-hearted ecumenism nor mistaken judgmentalism. It’s a matter of logic.

At the beginning of his Letter to Titus, the Apostle Paul urges new bishops to hold fast to the true message they have been taught. Doing so, they “will be able both to exhort with sound doctrine and to refute opponents.” Paul, of course, does not discuss the logic of genus and species. But St. Thomas Aquinas, whom the Church calls “The Common Doctor,” most surely does. Thus he teaches “In the mind, genus is prior to what it contains. But nothing is prior to God either really or mentally. Therefore God is not in any genus” (ST I, q. 3, a. 5).