The instrument now known as the baroque lute was commonplace in Bach’s Germany. Owing to the fact that most lutes were cheaper and more portable than keyboard instruments, its popularity had remained intact for the centuries in which it had been the ideal means of accompaniment for amateur singers. The instrument, while retaining the shape and timbre of its earlier forbearers during what was perhaps the height of its popularity in the 17th and early 18th centuries, had evolved substantially to reach the form it took on in Bach’s day. Before the middle of the 17th century lutes across Europe, while differing in other aspects such as the number of strings, were tuned in similar ways. This method of tuning-- 4ths around a central major third-- was described as early as 1483 in Johannes Tinctoris’s De inventione et usu musicae. Throughout the course of the 1600s, however, the need for an extended bass register prompted the addition of lower strings to the lute. There were so many strings that in fact a player’s fretting hand could not claim them all, and so the free-floating strings, under which there was no fingerboard, were most often tuned in a descending diatonicism that was adjustable based on the key of pieces. It was these additional basses which probably led to the elimination of the 4ths-around-a-3rd tuning, which was replaced in time by an open d minor tuning above the lower, diatonically descending bass strings (this tuning was by no means, however, universally accepted and the traditional tuning of 4ths was maintained throughout Europe and most notably in Spain in the form of the vihuela and baroque guitar, which later would pass on their open-inconsonant genes to the modern guitar).
Berlioz’s famous words stating that only those who play the guitar well can compose for it are doubly true for the baroque lute, which by this time had developed several tablature notational systems which varied from region to region. These tablature systems are one of the reasons why solo lute music continued to be written mainly by esteemed lute players of the day, and also a reason why the lute music of J.S. Bach stands out as an anomaly.