"...partitive exegesis: the common patristic stratey of determining whether a biblical passage is speaking of the Son of God in terms of his deity or in terms of his humanity. (Matthew Y. Emerson and Luke Stamps, "On Trinitarian Theological Method," in Keith S. Whitefied, ed., Trinitarian Theology: Theological Models and Doctrinal Application, p. 116)
In the supposed modern retrieval of trinitarian orthodoxy, certain trends in academia has started to make its way into Reformed circles as they lure people to the thoughts of Thomas Aquinas. This supposed ressourcement in part seems to be a re-reading of classical theology using a Thomistic framework, and this fiters into one's hermeneutics and exegesis of the text of Scripture.
As defined by Matthew Emerson and Luke Stamps, "partitive exegesis," a word that was not present during most of Reformed history, is reading Scripture about Jesus Christ, then asking the question, "Is this talking about Jesus in his divine nature, or Jesus in his human nature"? In a certain sense, the question is innocent. After all, if you believe Jesus has two natures: one human and one divine, then certainly when you read for example that Jesus slept, you might want to ask whether this means the divine nature can sleep. But is the question really that innnocent?
Exegesis is the interpretive task whereby the meaning of a text is derived from the text itsef. It is a literary endaevor, as it deals with texts in contexts. In order for an interpretive process to be exegesis, the meaning of the text has to be read out of ("ex-") the text of Scripture. The oppposite of exegesis is eisesegesis, where meaning is read into ("eis-") the text of Scripture. Now, for a long time, the term used to describe Protestant exegesis of Scripture is "Grammatical Historical (G-H) Exegesis," where attention is paid to the grammar and the historical context of any text of Scripture. As God communicates in words through the Word, meaning is seen to be found in the words inspired by God, and G-H exegesis is the highest compliment paid to the primacy of the written word in Scripture. An expansion of G-H exegesis is Redemmptive-Historical (R-H) exegesis, where Reformed exegetes point out the progressive revelation of Scripture, with Scripture interpreting Scripture. All of such progression in one unified Word brings forward God's plan of redemption, the one plan in both the Old as well as the New Testaments. Through exegetes and bibical theologians such as Gehardus Vos and Herman Ridderbos, this canonical reading of Scripture can be indeed seen to emerge organically from Scripture itself. G-H and R-H are not, as some might think, competing methods of interpreting the Scripture. Rather, R-H expands upon the insights of the G-H method, emphasizing that Scripture's way of interpreting itself must be seen and utilized by us as well.
If exegesis is to read meaning from the text of inspired Scripture, then there are limits to what is exegesis and what is not exegesis. It is from the exegesis of Scripture that we arrive at fragments of biblical truth — what the Bible teaches in particular texts. While we acknowledge that God's truth is indeed whole, nevertheless, an examination of the text of Scripture itself does not grant us this whole truth. The discipline of systematic theology therefore is meant to eludicate biblical truths. Systematic theology builds upon the fragments of biblical truth, and seek to systematize them and in so doing smooth out any flaws in our exegeses. Systematic theology is necessary for the Christian to know the unity of God's (ectypal) truths, but it is itself not exegesis. One is not doing exegesis when one is engaged in systematic theology. Rather, one begins with truths arrived at via exegesis, and then synthesize the biblical system of truth, the "pattern of sound words" (2 Tim. 1:13), from them. In order for something to be truly biblical, founded on Scripture, sound exegesis must be at the base of one's systematic theology.
It is on this note that we look at this thing called "partitive exegesis." Does this "exegesis" derives its truths from the text of Scripture? The obvious answer is no. It calls us to ask a question that is not found anywhere in that text. On this answer alone, we must reject its label of being "exegesis." But I have said that the question is "in a sense innocent," haven't I? Yes, when we are trying to synthesize biblical truths into a coherent system. "Partitive exegesis" is therefore not exegesis but theologizing. But, if the question should be asked anyway, why the concern over terminology? The concern comes about because of how easy it is to confuse one's theology with Scripture. If it is seen as exegesis, then one has placed the usage of this "exegesis" beyond criticism. Anyone who criticizes any use of this "partitice exegesis" is seen to be not truly interpreting Scripture, being tarred with the slur "biblicist." But if the issue is over systematic theology, then no view is considered as a "default" view. Contested views have to be argued and debated, where both sides can appeal to Scripture, and Christians have to deliberate over which view is more faithful to Scriipture.
This adoption of "partitive exegesis" is therefore a scourge to the Reformed churches. Even if the views adopted by the promoters of "partitive exegesis" are true, the very concept should be rejected. It is a terrible practice to prejudice your views as the default "biblical" view, and demand that anyone who rejects your view must prove it on your own terms using your own prejudiced method. That is certainly one way to avoid debate, but it is not a way that glorifies God or His truth.
ADD: And just to show why Thomists do not get it, here is a tweet from Joshua Sommers:
Right, but to presuppose the nature of Scripture in reading Scripture is to necessarily presuppose something of the nature of God, since Scripture is what it is in virtue of God. Agreed?— Josh Sommer (@1689Broadcast) October 29, 2022
Sommers confuses what the Reformed Scholastics term the Principium Cognoscendi (The beginning of knowing) and the Principium Essendi (The beginning of being). No, nobody "presuppose(s) something of the nature of God" when reading Scripture. We know who God is only from what Scripure tells us who He is. To believe something of God not taught by Scripture is called "idolatry."