Chapter IV - 2
It seems to us that the salient features of Thomism that give it its particular character are these: First, and most important, is the identification of God with pure being or pure existence (Latin: esse; = Greek: einai). É. Gilson, on whose presentation of Thomism we have to a certain extent relied, remarks that this is St Thomas Aquinas’ great insight and stroke of genius. Be that as it may, it is not an Orthodox approach to the Holy Trinity. For example, St Maximos the Confessor asserts, following St Dionysios the Areopagite, that God is not being, but the source of being. As he says in the Ambigua (Peri Diaphoron Aporion) 10, 38:
Whence, saying that the Divine exists, we do not say how it exists. And for this reason we say in its regard the ‘is’ and ‘was’ simply and indefinitely and in an unrestricted manner. For the Divine is unreceptive of every definition and concept, on account of which not even predicating existence of it do we say that it exists. For out of it [is] existence, but it is not that very existence. For it is beyond even existence itself, in either a qualified manner or simply, both spoken of and thought. If [we consider existence] in a qualified manner, and not simply, [then] beings have existence, just as [they are subsumed] under the where they are on account of their position and on account of the limit of their reasons (logoi) according to nature, and just as they will be completely receptive of being subsumed under the when they are, on account of the beginning.
This might seem to be a very Scholastic place for us to start discussion of the anthropology of St Thomas Aquinas. However, it does seem to us that the point of divergence of St Thomas Aquinas from the Orthodox Fathers is here, and that much of the particular or peculiar character of Thomism arises from this basic move of St Thomas.
For what St Thomas does is focus in his philosophy on being.
St Thomas makes a second move of the greatest importance both to the character of his philosophy and to his anthropology: he asserts very strongly that man naturally can know beings only by sense-perception: from that sense-perception, man abstracts by an act of the intellect the concept which defines the essence of that being. This of course is St Thomas’ realism. God is pure being; there is a hierarchy of participations in the being of God among God’s creatures, the created beings. Man can only know beings on the basis of sense-perception and on the basis of the abstraction of concepts from that sense-perception; and by the use of reason working propositionally with those concepts, man comes to know the essences of beings, and, indeed, all the truth that he is naturally capable of apprehending in this life.
The next characteristic of St Thomas’ philosophy is its rationalism. We have already remarked in Chapter I on the intense preparation in logic of the high mediæval Scholastic, comparable to the preparation in mathematics of a physicist at a leading university in the United States today. St Thomas assimilated this training in logic; he is an expert in the philosophical analysis of concepts. This mediæval technique is often disparaged nowadays even among professional philosophers. We do not mean to disparage it.
One simply cannot understand post-mediæval or modern philosophy properly without understanding mediæval philosophy. Modern philosophy is largely a reaction against mediæval philosophy, but, that being so, it can only be understood properly by reference to mediæval philosophy: the positions of modern philosophy are intelligible only when considered as reactions against mediæval philosophy, culture and faith.
It seems to us that St Thomas, influenced by his studies in logic and by the intellectual culture of the High Middle Ages, adopted a very rationalistic outlook, especially in his psychology of man. This outlook might not only be called rationalistic but intellectualistic.
Join this rationalism to the very systematic nature of St Thomas’ thinking, and you begin to delineate a portrait of Thomism, one that manifests its particular physiognomy: God is pure being; all beings participate in the being of God in a hierarchy of participations; knowledge is available to man only on the basis of the sense-perception of sensible beings and on the basis of the abstraction of universals from that sense-perception; this abstraction is treated in a rationalistic and intellectualistic way; the philosophy and theology are developed in a very rationalistic and systematic fashion.
Add to this the particular or peculiar character of Latin as opposed to Greek: Latin is a simpler language than Greek, and the concepts expressed in it are simpler. Moreover, St Thomas’ Latin is very simple: unusually for a philosopher, he does not present difficulties in his language, but in his metaphysics, derived from Aristotle. The reason for this simplicity is surely St Thomas’ training in logic.
This is the Thomist system. Many of St Thomas’ theological positions are acceptable to the Orthodox: no one would deny in the Orthodox Church that angels exist, and probably there is not much wrong with St Thomas’ theology of angels, unless you might want to quibble that it is not true that each angel is its own species. It is not so much in the formal content of St Thomas philosophy and theology that its particular or peculiar character arises but in the aspects of it we have just outlined: the identification of God with pure being; the denial of the possibility of knowledge apart from sense-perception followed by abstraction from sense-perception; the great rationalism; the very systematic nature of the philosophy and theology; the very simple, straightforward language and presentation.
Of course this is not to deny that St Thomas has positions that are unacceptable to the Orthodox Church.
Nor is it to deny, emphatically not, that much of the content of St Thomas, especially in areas where he appears to be following St Dionysios the Areopagite and especially in his anthropology where he is following the earlier Neoplatonizing philosophy of St Augustine, has undergone a reinterpretation on the basis of the characteristics we have just mentioned and on the basis of St Thomas’ Aristotelianism, so as to produce a system that is both formidable and logically coherent—and quite alien to the spirit of the Fathers of the Orthodox Church.
That is another characteristic that gives St Thomas’ system its particular or peculiar character: the reinterpretation by St Thomas of his sources, including his Greek and Latin Patristic sources, so that while he ostensibly retains their content, he redefines that content on the basis of his systematic, rationalistic Aristotelianism in such a way as to give a quite different character to that content from the character that it has in its sources.
The final characteristic of Thomism is its very great intellectual depth.
 Migne 91, col. 1180D.
 It should be noted that we translate esse (Latin) or einai (Greek) sometimes by being and sometimes by existence, according to the context. Thomist scholars sometimes translate esse by act of being; this distinguishes it from ens, being as referring to a concrete existent object. Being and existence are to be identified. They are of course to be contrasted with essence substantia or essentia; = Greek: ousia). Essence is to be understood in the context of Scholastic philosophy as that which confers knowability or intelligibility on an object. It is comparable to the reason (logos) of an object of sense of the Greek Fathers. In Classical Greek philosophy, the definition of a thing was precisely that which conveyed a complete account of the thing’s essence. (Latin: substantia or essentia; = Greek: ousia). Essence is to be understood in the context of Scholastic philosophy as that which confers knowability or intelligibility on an object. It is comparable to the reason (logos) of an object of sense of the Greek Fathers. In Classical Greek philosophy, the definition of a thing was precisely that which conveyed a complete account of the thing’s essence.