The Symbol of Chalcedon is one of the more important historical and theological documents of the church. If you've never heard of it, you should really read more about it.
But this post isn't about the theological and historical importance of the Symbol of Chalcedon (which dates back to Oct 22, 451 AD/CE). It's about the difference between αλλα and δε.
Creeds, confessions, and other statements of faith, by their very nature, attempt to be precise with their language. Words and phrasing are chosen to convey a particular point in language as unambiguous as possible. So even though the Symbol of Chalcedon dates around 400 years after the New Testament was written, the Greek version is still helpful to us in considering use of conjunctions. The text below conforms to Drobner, The Fathers of the Church: A Comprehensive Introduction (amazon.com), pp. 487-488 as much as possible. I took the Greek from the CCEL version of Schaff's Creeds of Christendom and fixed some typos and rearranged a few words to (upon a quick visual comparison) match the Greek presented in Drobner. The English is that of Jaroslav Pelikan and Valerie Hotchkiss, eds., Creeds & Confessions of Faith in the Christian Tradition, (amazon.com) vol 1 p. 181; though note I've rearranged some lines so that the English content is in the order of the Greek content.
I've made statements involving δε blue, and the one statement involving αλλα red. Note the differences between them.
|Ἑπόμενοι τοίνυν τοῖς ἁγίοις πατράσιν ||So, following the saintly fathers, |
|ἕνα καὶ τὸν αὐτὸν ὁμολογεῖν υἱὸν ||the confession of one and the same Son, |
|τὸν κύριον ἡμῶν Ἰησοῦν Χριστὸν ||our Lord Jesus Christ |
|συμφώνως ἅπαντες ἐκδιδάσκομεν, ||we all with one voice teach |
|τέλειον τὸν αὐτὸν ἐν θεότητι ||the same perfect in divinity |
|καὶ τέλειον τὸν αὐτὸν ἐν ἀνθρωπότητι, ||and perfect in humanity |
|θεὸν ἀληθῶς καὶ ἄνθρωπον ἀληθῶς ||the same truly God and truly man |
|τὸν αὐτὸν ἐκ ψυχῆς λογικῆς καὶ σώματος, ||of a rational soul and a body; |
|ὁμοούσιον τῷ πατρὶ κατὰ τὴν θεότητα, ||consubstantial with the Father as regards his divinity, |
|καὶ ὁμοούσιον ἡμῖν τὸν αὐτὸν κατὰ τὴν ἀνθρωπότητα, ||and the same consubstantial with us as regards his humanity |
|κατὰ πάντα ὅμοιον ἡμῖν χωρὶς ἁμαρτίας· ||like us in all respects except for sin; |
|πρὸ αἰώνων μὲν ἐκ τοῦ πατρὸς γεννηθέντα κατὰ τὴν θεότητα, ||begotten before the ages from the Father as regards his divinity |
|ἐπ᾽ ἐσχάτων δὲ τῶν ἡμερῶν ||and in the last days |
|τὸν αὐτὸν δἰ ἡμᾶς καὶ διὰ τὴν ἡμετέραν σωτηρίαν ||the same for us and for our salvation |
|ἐκ Μαρίας τῆς παρθένου τῆς θεοτόκου κατὰ τὴν ἀνθρωπότητα, ||from Mary, the Virgin God-bearer, as regards his humanity; |
|ἕνα καὶ τὸν αὐτὸν Χριστόν, υἱόν, κύριον, μονογενῆ, ||one and the same Christ, Son, Lord, Only-begotten, acknowledged |
|ἐν δύο φύσεσιν, ||in two natures |
|ἀσυγχύτως, ἀτρέπτως, ἀδιαιφέτως, ἀχωρίστως γνωριζόμενον· ||which undergo no confusion, no change, no division, no separation; |
|οὐδαμοῦ τῆς τῶν φύσεων διαφορᾶς ἀνῃρημένης διὰ τὴν ἕνωσιν, ||at no point was the difference taken away through the union, |
|σωζομένης δὲ μᾶλλον τῆς ἰδιότητος ἑκατέρας φύσεως ||but rather the property of both natures is preserved |
|καὶ εἰς ἓν πρόσωπον καὶ μίαν ὑπὸστασιν συντρεχούσης, ||and comes together into a single person and a single subsistent being; |
|οὐκ εἰς δύο πρόσωπα μεριζόμενον ἢ διαιρούμενον, ||he is not parted or divided into two persons, |
|ἀλλ᾽ ἕνα καὶ τὸν αὐτὸν υἱὸν καὶ μονογενῆ, ||but is one and the same only-begotten Son, |
|θεὸν, λόγον, κύριον Ἰησοῦν Χριστόν· ||God, Word, Lord Jesus Christ, |
|καθάπερ ἄνωθεν οἱ προφῆται περὶ αὐτοῦ ||just as the prophets taught from the beginning about him, |
|καὶ αὐτὸς ἡμᾶς ὁ κύριος Ιησοῦς Χριστὸς ἐξεπαίδευσεν ||and as the Lord Jesus Christ himself instructed us, |
|καὶ τὸ τῶν πατέρων ἡμῖν παραδέδωκε σύμβολον. ||and as the creed of the fathers handed it down to us. |
So, what are the differences, at least in the above context, between αλλα and δε? Well, working on the general assumption (via Heckert (amazon.com)) that δε is a marker of development and αλλα is a marker of contrast, we can note the following:
The first instance of δε: First, this is a μεν .. δε statement, which clues us in even more that these three lines are related in some way. Second, note the chronology: Christ was begotten "before the ages from the Father" and "in the last days for us and our salvation". The creed is speaking to the begotten-ness of Christ's divine nature and human nature. Both go together; there is development and comparison happening here. The μεν .. δε statement is a spectrum speaking as to the whole of the begotten-ness of the natures of Christ. There's no way this could be comparably (and as unambiguously) written using αλλα instead of δε.
The second instance of δε: The context of this instance is confirmatory; both natures of Christ are distinctly preserved and not co-mingled. The gathering of the natures in one person did not cause them to unite into one nature; "the property of both natures is preserved". The two distinct natures are present in one single person as the following και (which is generally 'additive' according to Heckert (amazon.com)) tells us. The δε statement is used to confirm that both natures remain separate; it is the developmental hinge in moving from two separate natures (lines previous to δε) into the και statement that these two natures are contained in one "subsistent being".
The instance of αλλα: This is a somewhat standard "not this, but that" instance of αλλα. The vast majority of New Testament and Apostolic Fathers instances of αλλα are of this kind. But the immediate context is important. The discussion of two natures precedes and has just developed into two natures/one person. The αλλα statement now unambiguously states that this is not two persons, but is one person. This is not development, this is contrasting the negated option with the positive option (in this case a direct false/true comparison) to make the αλλα phrase prominent. Considering the history of the doctrine of the nature(s) and person(s) of Christ until this point, which was all over the board (two natures/two persons, one nature/two persons, one nature/one person, etc.) this statement is clear, forceful and unambiguous. Not one nature, but two. Not two persons, but one. The following summary statement (last four lines of the symbol) are equally strong, noting that two natures/one person is grounded in the prophets (Hebrew Bible), was taught by Jesus (New Testament) and handed down this way from the fathers (tradition).
Now, it could be argued that there isn't much difference between the second δε and the αλλα. It is true, their immediate functions in these contexts are similar. At this point, I'd argue that the δε statement, especially with the και following, is largely developmental. It is the shift from speaking of natures to speaking of persons. The αλλα statement doesn't do that; it is more focused on making clear that Christ is one person, not two, even though he has two natures, not one.
Aren't conjunctions fun? Now, if αλλα and δε are important in contexts like the Symbol of Chalcedon; how important is is to have a general understanding of the discourse function of conjunctions when reading the Greek New Testament?