Dr. R Scott Clark is a proponent of Scripture-only worship, which is very similar but still distinct from Exclusive Psalmody. In this two posts here and here, he briefly argues for his position of Scripture-only worship, a position which he expounded in some detail in his book Recovering the Reformed Confessions. Lane Keister has posted two responses, with the former being replied to by Dr. Clark.
I have previously responded to a pamphlet promoting Exclusive Psalmody here, and I do not think my position has changed much since. In this light, I think that Lane Keister's second response bring up some of the points I would have brought up if I were in his shoes.
First of my objections to Clark's position is the translation problem. All Bibles in English and any language except Hebrew (OT) or Greek (NT) are translations, and all translations are interpretations. While the so-called Functional Equivalence (F-E) crowd used that to advocate for pure meaning translation, as if meaning can exist apart from words, the Formal Equivalence model is simplistic, as if languages function like codes. All Bible translations therefore have lexical interpretations in them, and the good translations attempt to have only lexical interpretations and not "meaning" interpretations found in those translations following the F-E model.
Within the good translations and not-so good translations of the Bible we have a variety. The relevance this has for both Exclusive Psalmody (EP) and Scripture-only (S) positions is that there already is some form of interpretation or paraphrase depending on the version of Scripture that is followed. For example, for Psalters, are we going to have a ESV-Psalter versus the NAS-Psalter versus the KJV-Psalter? If these are all acceptable, then we are essentially saying that interpretation/ paraphrase is acceptable as long as the words convey the meaning of the Psalms. The only thing that the EP/ S crowd is fighting for is limiting the quantity of interpretation/ paraphrase to the bare minimum. After all, no Reformed Christian holds that we are to sing non-Scriptural hymns and songs to God. The controversy is thus the amount of interpretation/ paraphrase acceptable.
Secondly, since Reformed worship limits itself to what is biblical, the difference I would have with Dr. Clark is that he denies that rearrangement and systematization of biblical truths and our biblical responses to these truths cannot be sung. But surely, are we saying that we can confess biblical truths like the Trinity but not sing them? If the concern is about imposing them on the congregations, the same could be said of the creeds and confessions. For most certainly, these are to be confessed by the entire congregation, yet none of the Church's creeds and confessions are directly lifted from Scripture as a single unit. For example, you would not find the Apostle's Creed or the Nicene Creed in Scripture. You will find the contents, but not the form. Similarly, when we sing biblical truths of which the form is not found in Scripture, but the contents are, are we not doing the same?
Lastly, I would be very interested to know if Dr. Clark approves this song/ Psalm(?) by Deb Fung entitled For You Created, based ad-verbatim on almost the whole Psalm 139 as found in the NIV, and the reason why or why not: