From a Trinitarian perspective, does the term 'only begotten Son' make sense outside of the concept of the incarnation? From a Trinitarian perspective, does the term 'only begotten Son' make sense outside of the concept of the incarnation? If so, how? If not, why not?

The Niceno–Constantinopolitan Creed states (in part):


  We believe...in one Lord Jesus Christ, the only-begotten Son of God, begotten of the Father before all worlds... (emphasis added)


My question in extended form: Is the 'begotten-ness' eternal if and only if the incarnation is viewed from an eternal perspective as well (our sense of what begotten means would consequentially be inextricably linked to the incarnation) or is there some logic in conceiving that somehow a temporal locus of the incarnation imparts a distinction between it and 'eternally begotten'?

I imagine this is the sort of issue Thomas Aquinas would have considered - if so can someone direct me to how he addresses the issue.

I am also interested in the views of any other relevant trinitarian theologians as well.

This question: Is there any proof from the Bible that the second Person of the Trinity was the Only-begotten Son of the Father before His incarnation? is related but distinct.
Aquinas addresses the question from different angles a number of places in the Summa Theologica, in various parts of the &quot;Treatise on the Most Holy Trinity&quot; (First Part, Questions 27–43).
The fundamental question is answered more or less directly in Question 27, &quot;The Procession of the Divine Persons&quot;. Article 2 of this question, &quot;Whether any procession in God can be called generation?&quot;, talks about what it might mean to say that the Son &quot;is begotten by&quot; the Father. Thomas' answer is:

... We must observe that generation has a twofold meaning: one common to everything subject to generation and corruption; in which sense generation is nothing but change from non-existence to existence. In another sense it is proper and belongs to living things; in which sense it signifies the origin of a living being from a conjoined living principle; and this is properly called birth.
Not everything of that kind, however, is called begotten; but, strictly speaking, only what proceeds by way of similitude. ... the procession of the Word in God is generation; for He proceeds by way of intelligible action, which is a vital operation:—from a conjoined principle (as above described):—by way of similitude, inasmuch as the concept of the intellect is a likeness of the object conceived:—and exists in the same nature, because in God the act of understanding and His existence are the same, as shown above. Hence the procession of the Word in God is called generation; and the Word Himself proceeding is called the Son.

The Son, in other words, is &quot;begotten&quot; not in virtue of the Incarnation, but because the Son is the Word of God proceeding from, and in that sense &quot;begotten by&quot; (one could say &quot;generated by&quot;), the Father.
There are a few other places where Aquinas discusses different aspects of the question (such as &quot;Is it appropriate to call the Father 'unbegotten'?&quot;), but this is the clearest exposition of Aquinas' actual position, and it appears from his discussions as a whole to be a standard Trinitarian answer.