On this, the Feast of St. Augustine, it is fitting to meditate on an Augustinian passage. There is an interesting passage in On Christian Doctrine that suggests a way to think about the Incarnation. Commenting on the NT text, "the Word was made flesh and dwelt among us," Augustine writes:
In order that what we are thinking may reach the mind of the listener through the fleshly ears, that which we have in mind is expressed in words and is called speech. But our thought is not transformed into sounds; it remains entire in itself and assumes the form of words by means of which it may reach the ears without suffering any deterioration in itself. In the same way the Word of God was made flesh without change that He might dwell among us. (Bk 1, Ch. 13, LLA, 14; tr. D. W. Robertson, Jr.)
What we have here is an analogy. God the Son, the Word, is to the man Jesus of Nazareth as a human thought is to the sounds by means of which the thought is expressed and communicated to a listener. Just as our thoughts, when expressed in speech, do not become sounds but retain their identity as immaterial thoughts, so too the Word (Logos), in becoming man, does not lose its divine identity as the second person of the Trinity. Thought becomes speech without ceasing to be thought; God becomes man without ceasing to be God.
Unfortunately, there are significant points of disanalogy which render Augustine’s analogy unsuitable for proving the coherence of the Incarnation.
1. Although speech is an embodiment of thought, Jesus is not an embodiment of the Word because Jesus is not a mere body, but a body-mind complex. In the Incarnation, God the Son does not merely assume a human body; He assumes a human body-cum-mind. Otherwise, God the Son would not become fully human.
2. The Incarnation implies a claim of identity: Jesus is God. The identity relation, however, is distinct from both the embodiment and the expression relations. Identity is symmetrical: if x = y, then y = x. But embodiment is asymmetrical: if x embodies y, then it is not the case that y embodies x. The same goes for expression: if a certain form of words expresses my thought, then it is not the case that that thought expresses my form of words.
3. Incarnation is a one-one relation whereas embodiment and expression are one-many. Although Jesus is the unique incarnation of God the Son , not one avatar of deity among many, different spoken sentence tokens – indeed, different spoken sentence tokens of different sentence types – express or embody one and the same thought. Thus one and the same thought is expressed by the following four sentence tokens of three sentence types: The sea is blue; the sea is blue; Deniz mavidir; Die See ist blau.
4. A thought is not a mind, but an accusative (direct object) of mind. But God the Son is a mind. Thus the embodiment is different in the two cases.
To sum up. We know that thoughts get embodied in speech. It is therefore possible that thoughts get embodied in speech. So if the Incarnation were a special case of the general phenomenon of thought getting embodied in speech, then we would have a proof of the possibility of the Incarnation. But I have just shown that the Incarnation is not a special case of the general phenomenon in question. Therefore, Augustine’s analogy, as fascinating as it is, is unsuitable as a proof of the possibility of the Incarnation.
Could a Christian respond by saying that the Incarnation is just a sui generis phenomenon that cannot be subsumed under any extant model or any known sort of relation? Yes, but then the question as to how it is possible goes unanswered. Must the Christian be troubled by the possibility question? The Christian could say: the Incarnation is actual therefore it is possible; and since it is possible, there must be some answer to the question as to how it is possible even if no one has ever given a good explanation of how it is possible. Thus the Christian could stand pat on what he takes to be the fact of the Incarnation. But this will not satisfy the philosopher who will point out that the fact of the Incarnation is not like the fact of motion. A Zenonian who denies the possibility of motion will be confronted with what all admit is a fact, namely, that things move. But that God became man in Jesus of Nazareth, even if a fact, is one that is rather less widely admitted.
There is also this metaphilosophical question: since one cannot prove anything with an analogy, why give them at all? To persuade people who lack the intellectual acumen to realize that they lack probative force? Do they belong only in rhetorical contexts?
If your goal is merely to convince someone of somthing, to effect a change in his beliefs, then it doesn't matter whether the arguments and analogies one gives are probative. From the point of view of rhetoric, any argument is a good argument if it is deemed persuasive by the addressee. But from the point of view of truth, only probative arguments count.