I noticed as I listen to Bach's Chaconne in D minor, that not only do I hear a lament bass when Bach is in D minor but also when he is in D major. But why? It isn't like the lament bass is normally used in major. I know that Bach's chord progression isn't quite a lament bass by itself, but it is certainly based upon it. Here is where the chaconne starts being in a major key for a while before it goes back to being in D minor(which is about 11 minutes into the video):
Here is my hypothesis as to why I hear a major key lament bass:
Minor key preparation
To put it simply, the fact that Bach is using a progression based on the lament bass when he is in D minor and the nature of the chaconne being variations upon a chord progression means, that even when Bach goes to D major for a while, all those variations upon the lament bass in the first D minor section prepare us to hear the descending bass in the D major section as also being a lament bass, even though the lament bass is usually only heard in minor and Bach is sticking with harmonies native to D major.
A harmonized descending scale in major uses a passing dominant chord in the same place as the passing chord in the lament bass, with the only difference between the passing chords being that in the lament bass, it is minor, and in the harmonized major scale, it is, well, major. But I think the reason Bach is able to get this lament bass sound in D major is because he used it a bunch of times in D minor, so the minor key acts as a preparation for the parallel major key harmonically speaking.
But is that why I hear the descending bass in D major as a lament bass? Does it have anything to do with the minor key variations that came before?