When the chisels chipped into the Wall and the first Trabant nosed into West Berlin in 1989, who could have predicted that one of the direct consequences of Germany's reunification would be the tremendous efflorescence of Bach-family studies that we are now enjoying? Almost overnight, it seems, East German library vaults flew open and their contents were sifted forensically for the first time, war-looted archives began to return at a snail's pace from Yerevan, Kiev and other eastern places to their original homes in Germany, East German scholars could travel with greater freedom, and Leipzig established itself as the unquestioned major centre for Bach studies. Discoveries and re-evaluations of Bach and his family are still being made at a remarkable pace: every new issue of the Bach-Jahrbuch is bigger and richer than the last, and each one offers new perspectives, new material and new information. The ongoing production of a complete critical edition of Carl Philipp Emanuel Bach's works – a collaboration between German and American scholars that is fuelled by the munificence of the Packard Foundation – is yet another ramification of post-Cold-War engagement between musicologists from both the East and the West. Published in Silicon Valley, edited in Harvard, printed handsomely and sold at a price that is almost within the pocket of an impoverished student (the most expensive volume costs $30), this edition is a phenomenal success. The timing of its production could not be more appropriate, as the publication of all the volumes is scheduled to be completed by the year 2014, the tricentenary of Emanuel's birth.

Among the works appearing in print for the first time are the twenty-one settings of the Passion that C. P. E. Bach produced during his Hamburg years (1768–1788). These works are essentially new additions to the C. P. E. Bach work-list: they were unknown to Alfred Wotquenne, whose Thematisches-Verzeichnis was published in 1905, and while E. Eugene Helm displayed some knowledge of them in his Thematic Catalogue of the Works of Carl Philipp Emanuel Bach (New Haven and London: Yale University Press, 1989), his descriptions were somewhat hazy. Emanuel had, of course, composed church music both before and during his time at the court of Frederick the Great, where he was in service from 1740 to 1768, but his attachment to five churches in the Hanseatic port of Hamburg necessitated a much more rigorous approach, and a spate of compositions ensued, including an annual setting of a Passion. The choice of the Passion narrative each year followed biblical order: the Gospels of Matthew, Mark, Luke and John were set successively in a four-year cycle. While a number of these musical settings had been lost or existed in fragmentary form, the re-emergence of many archival sources from the Berlin Sing-Akademie – brought back from their post-war exile in Kiev – has re-energized this area of C. P. E. Bach studies to a considerable extent. We can now approach these new works with fresh eyes and ears.

On moving to Hamburg in March 1768, Emanuel – hoping to enjoy some freedom away from the court of a despot (enlightened or not) – was to be disappointed and constrained by the old-fashioned conservative attitudes of his new employers. He evidently got off on the wrong foot in 1769, writing his Passion according to St Matthew h782 when the cycle demanded a setting of St John's text, and producing a large-scale work which was composed in part by himself, but which also relied to a great extent on borrowings from his father's masterpiece of the same name, bwv244. This was unacceptable to Hamburg's authorities, and from 1770 he abandoned the modern oratorio style of Passions that included frequent reflective and poetical interpolations, to return to old-fashioned, fairly straightforward settings of the gospel texts. Unlike his father's Passions, Emanuel's twenty subsequent works are short in length, each lasting about an hour, with the narrative interrupted relatively infrequently by arias and choruses. There was a reason for their brevity: they were written not for a single performance on Good Friday, but for the first five Sundays of Lent, when they were heard in one of the five churches each week during the Sunday morning liturgy. Long, spacious, reflective works were not required. Chorales are frequent and prominent: they begin and end each work reviewed here. We know from the printed librettos that the congregation probably joined in with the hymns – contrary, it would seem, to the practice in Leipzig for Johann Sebastian Bach's Passions. The chorale harmonizations are to the point and effective, but somewhat bloodless when compared to those of J. S. Bach. The overall effect is plain and austere. The arias appear as breaks in the narrative rather than emerging organically – there is little or nothing of the immense emotional sweep and surge of his father's works – and we find no great dramatic scenes, or much evidence of scene-setting. Yet Emanuel's Passions are effective in their restraint, and they are all, to a greater or lesser extent, pasticcios. Indeed, both works under consideration here – the first of C. P. E. Bach's settings of each of the Passions according to St Mark and St John (and the first Passion settings in the series to be published) – were, effectively, written by other composers; they were only assembled and retouched by Emanuel.

The Passion according to St Mark (Passions-Musik nach dem Evangelisten Marcus) h783, first performed in 1770, is a shortened version of the Passion by C. P. E. Bach's Dresden contemporary Gottfried August Homilius and contains little or no original composition by Emanuel, apart from numerous small changes to the vocal line and declamation. Three chorales in the present text are not found in the version by Homilius. On this basis, there would be good grounds for excluding this work from the Complete Edition, were it not that Homilius's setting became the matrix for all of C. P. E. Bach's subsequent settings of the St Mark Passion. For example, in the fourth and last of these, h799 (1786), Homilius's gospel narration survives intact with few changes. Only some of the interpolations are new or borrowed from elsewhere, with Bach adjusting Homilius's music to accommodate the keys of the insertions. It is useful to have this lovingly prepared first version of the text in print, not only to compare with later versions, but also to see Emanuel at work, kneading and discarding Homilius's music in accordance with Hamburg liturgical practice and his own musical and aesthetic tastes.

The musical narrative of C. P. E. Bach's first Passion according to St John (Passions-Musik nach dem Evangelisten Johannes) h785, first performed in 1772, is from the 1745 setting by Georg Philipp Telemann, Emanuel's godfather and predecessor in Hamburg. The text is once again heavily reduced, cutting seven arias from Telemann's version. Any non-biblical interpolations in the form of ariosos or recitatives in Telemann's text are also removed. This version of the Passion incorporates music by Gottfried Heinrich Stölzel, J. S. Bach and Homilius, sometimes with new words, sometimes with the original retained. The most interesting case of a borrowed movement is J. S. Bach's chorus ‘Ruht wohl, ihr heiligen Gebeine’ from his Johannes-Passion, bwv245, which is used by Emanuel at the identical place in the narrative, but in which he makes significant alterations to the vocal text. Were these changes a personal response to the words by Emanuel? Or were they simply a way of asserting some form of creative ownership of the work?

C. P. E. Bach's procedure in assembling the Passion according to St John was to have an assistant prepare a short score of the biblical narrative and chorales of Telemann's original and to mark up this score showing where any interpolated arias, duets and choruses were to be inserted. The copyist would then prepare vocal and instrumental parts for the performers and – hey presto! – the Passion was ready to be rehearsed. Bach's preparatory scores of this work have survived, and there are some interesting facsimiles in this edition, not least a couple showing Bach's annotations and changes to the autograph of an aria by Stölzel. Clearly, Bach left no corner uncut. The Telemann text, again, became the basis for three future settings of the St John Passion, performed in 1780, 1784 and 1788; but in 1776, for a change, Bach used a setting of the St John Passion by Homilius.

Both these works are edited scrupulously and answer most of the questions one would wish to ask. They are illustrated with a number of apposite facsimiles, and there are useful tables to describe who wrote which part and what was omitted from Homilius's or Telemann's original texts. Although there is at least one recording of the final version of the Passion according to St Mark, it is difficult to imagine that any would join J. S. Bach's works in the general or even specialized repertory.

The opportunity to examine these scores, and indeed to view all the Passiontide music of C. P. E. Bach, provokes many questions about Emanuel's attitude to his church works. The first relates to his absorption of other composers' music. It has always been known that Emanuel, for his Hamburg church music, was unrestrained in the use of his father's manuscripts, many of which he owned. But the borrowing in the Passions is so extensive as to be remarkable and unusual. Did any other important eighteenth-century master after 1750 raid other composers' music so assiduously? Both Johann Christian Bach and Christoph Willibald Ritter von Gluck still recycled their earlier music in later works. But while self-borrowing is one thing, purloining on this scale is another. In this respect, Emanuel resembles an operatic pasticcio maker (at least in the Passion according to St John) in assembling a work from the arias of others.

C. P. E. Bach's no-nonsense approach presents a stark contrast to his father's highly personal and deeply felt attitude to the Passion text. Sebastian left his stamp on the Passion story; yet Emanuel, in his twenty-one works, appears to have scarcely left a mark. Ulrich Leisinger, in the General Introduction to these volumes, defends C. P. E. Bach by stating that in ‘the light of the four-year cycle, it would have seemed natural for works to be revived every few years; yet none of Bach's Passions is identical with its predecessors’. But can they really all be called Bach's Passions? And why did Emanuel Bach not wish to sing the age-old story with his own voice in at least one of the twenty-one settings? Was it perhaps a case of all passion spent?