Ever since I realized that this word moderato has a specific meaning -- actually more of an implication than a literal meaning -- I have been on the lookout for it. Beethoven does not use it in his piano sonatas, though I did find it in the Sonata for Piano and Natural Horn, where it is used for both the first and the third movements.
I just found it again in Op. 96 for Piano and Violin, the great G major Sonata, first movement. It changes everything to realize that the implication is that the beat is primarily lyrical rather than metric.
The issue of metric beats is a critically important one, since we learn at an early age to count quarter note beats. But not all meters should be considered divisible into quarter notes. Classical composers (through at least Brahms!) are very clear about when they want clearly delineated quarter note divisions and when they do not. A slur over a set of 4 sixteenths should be pronounced as articulating the beginning of a discernible four-note group whether or not it begins at a recognizable quarter note beat. But a succession of, say, seven sixteenths with no slur should be articulated as seven distinct units tunable according to the ear of the player, but not accented metrically.
The difference this makes is gigantic, nothing less. Likewise the technical demand this implies is gigantic. But the energy thus accessed is well worth the effort as is the humor. I thoroughly endorse this reading.
It may, indeed, be why the tempo is sometimes marked Allegro vivace: One aspect of the material will be metered in quarter note beats while another will not. Thus the material partakes of two different natures, not incompatible but totally different. It would account for the sforzati that sometimes occur on the beat in sixteenth-note passages. Why should they be there unless they are part of an essentially unaccented succession of notes?
The accents that we too readily impose upon everything we play give a false sense of security and keep us from noticing what is or is not happening. (By that I mean that they keep us from noticing how bored we get when we play metrically dentical measures one after the other.)
