Having now launched myself into Arthur Loesser's "social history," Men, Women and Pianos, I found myself fascinated with the way in which he works the rise of the Pietist movement into his account of the origins of the piano as we know it (basically, by way of the clavichord, which he views as the first keyboard instrument to allow note-by-note control of amplitude). Here is how Loesser sets the context for the origin of Pietism:
Seventeenth-century Protestant Germany offered spiritual contentment for the landed, the learned, and the logical; but many others were at a disadvantage.
Basically, Pietism emerged as a recourse for those "at a disadvantage" through the precept that "intense personal feeling" was more important than property, education, and logic. The title of his chapter captures both the sincerity and the awkwardness of this position:
"Feeling" Seems Better than Logic
What is the verb "seem" if not the expression of feeling-based evaluation, casting a tautological cloud over any attempt to read that title as a logical proposition (which may, indeed, have been the rhetorical intent behind formulating the text that way)?
Another way of examining this transition might be through current perspectives of social theory. The premise behind that context-setting sentence is that logic provided a path for being learned and, if not landed, at least in an advantageous position to do business with the landed. Those who embraced this premise believed, probably as an article of faith, that the objective world was the only world that mattered, if not the only world that existed. From this point of view, Pietism can be seen as grounded on the hypothesis that there is also a subjective world that, at least as far as any religious communion is concerned, was more important than the objective world. This is not to suggest that subjectivity was "discovered" somewhere around the turn from the seventeenth to the eighteenth century; but it did achieve a level of legitimacy that justified talking about it in the course of normal conversation.
Does this view of social history inform how we think of music history? My guess is that, while it may offer insights into religious life, it may be somewhat myopic where the practice of music is concerned. Loesser has a tendency to see a wide gulf between sacred and secular music that, for example, ignores the extent to which Luther himself saw the value of appropriating popular tunes for the singing of hymns. Albert Schweitzer's biography of Johann Sebastian Bach stresses this by quoting Luther as saying, "The Devil cannot have all the good tunes to himself!" Thus, while there may have been significant divisions of social strata over the practice of religion, those divisions probably narrowed (if not disappeared) where the practice of music was concerned. It is hard to imagine musical practice that totally disregarded the subjective world (although that may just be a result of contemporary thinking that accords equal status to the objective and subjective worlds).
Consequently, the idea that the performance of music should become more "expressive" as a result of the legitimation of the subjective is probably a red herring. More important may be a criterion that Loesser almost dismisses as an aside, which is the extent to which musical instruments have the same expressiveness as the voice. It is in the imitation of vocalization, so to speak, that the flexibility of dynamic control in the clavichord surpassed the keyboard instruments that preceded it. The success at achieving that flexibility could then drive further technical development that would lead to the piano as we now know it.