Marx's plea is for the combining of scholarly research and objective studies with the artist's intuition and expressive sensibilities. Griepenkerl insists on the certainty of the authenticity of Forkel and his students, despite the fact that these people lived 50 to 100 years removed from the lifetime of Johann Sebastian and, most importantly, at a time when all aesthetic forms, structures and media manufacture, techniques and sonorities underwent radical changes from those which formed the earlier world of Bach. Marx draws the curtain of certainty aside when he points to "the completely different path" of Carl Philipp Emanuel, whom Griepenkerl holds up as an intermediary handing down the undiluted performance style of his father. Today we recognise clearly that although Philipp Emanuel was to a certain extent a valuable repository of compositional and performance practices of his father's era, he had departed very significantly from those of his father's compositions. Emanuel retained devices and nuances of performance that emanated directly from the world of Sebastian, documented in his performance instructions in his book 'Essay on the True Art of Playing Keyboard Instruments' interspersed with his own forward-looking views and compositional style.  His own compositions demonstrate that he had moved into the current aesthetic, musical and social fashions of his own time — the mid-eighteenth century with its total departure from such concerns as polyphonic forms, contrapuntal concepts, and the techniques and sonorities of previous performance media. His way of life at the court of Frederick the Great, who was a great champion of the Enlightenment, housing such advanced thinkers as Voltaire, was the antithesis of Sebastian's entrenched life in the Church despite the latter's forays into public performance and an unsustained attachment to a court, along with some comparatively feeble connections with noble patrons.
Marx invites Griepenkerl to join him in the mine of the "ore of truth".
...We are not really opponents in the main, but allies; we work, like mine workers in different areas, perhaps in opposite directions, towards the same goal: the pure ore of truth. 
No answering response came from Griepenkerl. With Marx's reply, the correspondence ends. Griepenkerl was dead one year later; Marx's wished-for dialogue never took place. Had Griepenkerl written his reply to acknowledge his fellow "mine worker" as working towards a common goal and accepted Marx's offer of a dialogue between 'honest fellow-artists', the history of attitudes towards Bach performance might have been channelled into a more positive, less divisive course. It may have shed the requisite light upon the complex levels of the evolution of creative ideas, and their myriad influences on all thought, taste and performance manner, rather than confining principles of judgement chiefly within the boundaries of 'correctness' and imitative efforts. The ensuing expansion of views and penetration into each other's areas of concern — areas which appeared to be alien to each other — would have created an invaluable precedent and influenced, possibly accelerated, the amalgamation of scholars' and artists' efforts — an indispensable synthesis for well-recorded notetexts, treatises and media studies and for the wide-ranging additional requirements in the re-creative art of performance in general and in particular, of music of the past. The unbridged gap reflected in this correspondence widened in the late nineteenth and throughout most of the twentieth century creating alienation in the academic and performing communities. 
The significance of this correspondence of 1848 lies in the stance of these two major figures. Griepenkerl puts his faith in and confines it to the single, backward looking face of Janus; Marx acknowledges the inevitability of the existence of the forward-looking face and embraces both. With Marx, the totality of Janus is thereby restored. Griepenkerl was a product of the nineteenth century. He clung to the notion of 'Ur', of inviolable authenticity, the illusory beam guiding scholars and performer on to the rocks of a never-never land. He clove to a dogma of faith, believing in a static concept and practice unchanged by passage from culture to culture. He held — with desperation, on the occasion of the correspondence with Marx — to the blanket application of the 'ur' concept. Marx prefigures and anticipates the insight that has begun to penetrate the mainstream of thought of the later twentieth century. Or, one might say, Marx was already breaking the boundaries that sustained the dependence on the belief in the 'ur' platform. The deepening perceptions regarding the evaluation of concepts and the myriad factors that fructify and influence value judgements and structural forms arising from these have emerged from scientific disciplines chiefly of this century. One of these perceptions concerns the attitude towards 'ur', which is no longer regarded as a secure and unquestionable platform. This approach has infiltrated the musical community despite the still-existing aura of 'ur' that radiates in some sectors.
The two positions held by Griepenkerl and by Marx demonstrate a gap, which, in the course of the next hundred years expanded, causing sharp divisions and creating virtually unbridgeable territories. The scholarly editions of the Bach-Gesellschaft (1850-1900) co-existed with the flourishing romantic/virtuoso manner that was already practised well before 1819, by such figures in composition and performance as von Weber and Hummel. Amplified continuously, as in a great crescendo, the inflated Lisztian mode set a style that was long approved, but from which recoil began to appear already in Liszt's time, as expressed by Marx.
The Bach-Gesellschaft edition, the production of which spanned fifty years 1850-1900, provided the first systematically researched project of Sebastian's music by scholars, creating a precedent for the procedure of basing music publications on original sources. But the edition was mute regarding performance of the music. Only the comparatively sparse performance and embellishment indications conventionally noted by composers of Sebastian's era were reproduced, quite properly, according to the source material indications. On the one hand, the 'clean' pages heightened the contrast between the flamboyance of the typical nineteenth century performance editions and transcriptions. On the other hand, the scarcity and, in many cases, non-existence, of such indications acted upon literal-minded nineteenth and twentieth-century minds as an explicit, and to others as an implicit, direction to perform without any performance devices.  This linked up with the myth of objectivity and purity which came to the fore in the mid-late eighteenth century and was nourished to such effect as to spread an international faith in the belief that 'objective', 'clean' performance was the most authentic and most desirable. Such performance was deemed obtainable only with no input from or linkage with a performer of posterity. The dogma of objectivity/authenticity has supported all the diverse sects and applications, of which there have been many changing fashions, in the 'authentic' movement. But the thought that different eras produce varying notions of what constitutes authentic performance is put aside, as each successive version of 'authentic' notions and applications becomes fashionable, and takes its place as the latest approved stylistic manner. For several decades harpsichordists have been exchanging their previously approved harpsichords every 5 to 10 years for the next wave of harpsichords by newly approved harpsichord makers, regularly scorning the previous instruments. This continuous turnover is to some extent based on occasional improvements, but changing tastes are equally involved. It is time this issue, also, is addressed with the totality of view afforded by Janus.
Curt Sachs, the great musicologist of the era of richly burgeoning research in early music (roughly the second quarter of our century) wrote, referring to the aims of the editors of the Bach-Gesellschaft:
The purpose was not so much to be complete as to be correct, and to replace those numerous unreliable editions which left out, added and altered according to the personal taste of the 'editor' or to the contemporary mode...
Correctness also became more and more the password for the performance of ancient music... It would be wronging the men who were responsible for this attitude to reproach them with sterile literalism. Correctness to them was neither orthodoxy nor pedantry. Their point was to be faithful, not to "history" but to art. 
However, the belief that correctness constituted the "password for the performance of ancient music" omitted the complex conceptual orientation and aesthetic responses of the individual of the past and of succeeding cultures. Moreover, the forward-looking face of Janus was bypassed, ignored and even condemned. The omissions and taboos of the continuing Weltanschauung of succeeding cultures led to a condition of sterility arising from emphasis on manner and image and this, surely, was not Sachs's aim. The key word for this discussion is 'correct'. No one will deny the value of original sources as well as reliable historical treatises directed to period performance practice; all educated efforts towards their discovery and publication are beyond criticism and must continue. Sachs's work and that of others of his time propelled, without doubt, minute attention to original sources by well-equipped scholars which expanded explorations in manuscript sources and benefited performers. (Studies in original sources and/or their copies and copyists have also been a blessing for Ph.D. applicants; this kind of work provides endless subjects for Ph.D. theses, and reworking by succeeding generations till the end of time.)
Correctness became the guiding light superseding, as a supervising agent, all other facets that art involves. Notwithstanding Sachs's assertion that correctness was to be pursued for the sake of art, this emphasis came to mean correct art. At this point, the spectre of danger appears in full force. Art not only cannot thrive on a regime of correctness — it dies. This is not to say that an unending search for the concepts, applications and techniques of past eras is unavailing or unrewarding. Indeed, it is a preliminary step and mandatory as one kind of building material. But correctness remains a single building material; to found any art on claims of correctness removes it from the realm of art and places it in the realm of academic textbook-oriented history. So much more, intrinsically and externally, is involved in the production and in performances of art music. Curt Sachs was certainly correct in principle. But this principle has been disproportionately applied and, accordingly, misdirected in application, for correctness is relied on here as an overall protective blanket constituting aesthetic validity.
The stance of correctness is basically necessary, of course. But performance is more than an informed skill. Performance is an art and for art, correctness constitutes, at best, only a first step tool in the virtually limitless region of an artistic expression, whether that be related to a past or contemporary culture. When it is elevated to an absolute dogma, building a wall between artist and scholar — that is, between scholarly productions and the all-embracing needs of an artist and the production of a work in performance — then this stance is exaggerated and misdirected, posturing (in all sincerity as in many dogmatic faiths) as the ultimate means for artistic expression. The appeal to correctness in performance by posterity reflects a sense of responsibility towards the thought and expression of a past age which must be maintained. To this must be addedthe fullest study and appreciation of the kaleidoscopic hermeneutic processes at work in every performer from era to era.
The exhilaration of uncovering historical materials distracted and drew attention away from the unalterable fact that such materials as historical data remain, in essence, raw data. The collection of grapes does not represent wine; it is only after much fermentation, maturing and integration of many elements and processes that take place following the material product of the grape that the collection of grapes yields wine. The certainties of the twentieth century regarding authenticity are at last weakening in the face of more advanced thought. In the last twenty years or so, the younger generation has brought forward increasingly a reference to the fresh sight of the child who exclaimed, "But the Emperor is wearing no clothes!" Entering in some measure into a slowly-clearing view, this recognition is albeit still too limited and, sometimes, still biased. The long reign of certainty is now over. To observe that contemporary responses intermingle with value judgements and interpretive choices induces a first step in turning towards, and acknowledging, the realities of the present. With the commencement of this level of inquiry, so long overdue, we enter the domain that opens the possibility of the wider view that the backward and forward-looking face of Janus provides.
The desire for historical correctness promoted the notion of duplication for the sounds and textures of the past. In the realm of performance, such duplication represents imitation of period instruments and performance manner. The history of modern manufacture of and performance on period instruments begins with the early twentieth century. Arnold Dolmetsch was a special kind of genius who helped to initiate and kindle interest in seventeenth and eighteenth century music and instruments. His book on the music of this period  was one of the earliest systematic attempts of this century to enlighten the modern musician on the subject of 'early' music. Dolmetsch's manufacture of clavichords as well as his clavichord performances promoted interest in instruments and sonorities of earlier periods.
Dolmetsch's propagandising spread the movement for period instruments particularly in England. On the Continent, Wanda Landowska, the Polish-born Paris-based harpsichordist, was stimulating international interest in the harpsichord. After the Second World War she established herself and her ideas in the United States. At the time of her world fame she was hailed by many as the representative of authenticity in Bach performance, but not by Curt Sachs, who ridiculed her by implicit, but unmistakable, reference to "the lady".  Today she is, however, accorded the role of the mother of the harpsichord school. Sachs's derision was aimed chiefly at unstylistic aspects of her performance. Aside from these, was the actual instrument which she played a representative vehicle upholding her assertion of authenticity? Was it indeed authentic and did it replicate the sounds of the harpsichords in use in the first half of the eighteenth century? For it was the music of this period which made up her programmes. Perhaps an eye/ear witness of her performances and of her specifications for the manufacture of her harpsichords may be of interest here.
I was quite young at the time that Landowska arrived in New York in the late 1940s and was present when she performed Bach's Goldberg Variations at her opening recital there at the Town Hall. I had already spent years since age 14 in research in the study of period instruments and treatises and the latest findings in note texts and performance practice by the distinguished scholars of the time. By the late 1940s, I had developed my basic ideas regarding the concept, as well as structural and sonority aspects of Sebastian's music and was well practised in performing on the harpsichord, clavichord and organ. My own weekly series, at age 22, of six all-Bach recitals in New York  had at an early age given rise to a performing career in all-Bach programmes, but being still young and open-minded I respected her authority. When I arrived in London for my debut there in 1953 and remained to live in England, I needed a harpsichord, and, knowing that Landowska performed exclusively on Pleyel instruments, flew to Paris to order a harpsichord from them. I was well aware of Landowska's harpsichord pedals and her excessive use of sixteen foot, but her demands for the manufacture of the instrument were virtually unknown. Did I find an 'authentic' harpsichord modelled after any of the famous manufacturers of the eighteenth century? Alas, no. I was told at the Pleyel factory that Landowska's harpsichords were constructed entirely according to her personal specifications, with:
1) a metal frame — as is the piano
2) with piano strings
3) with keys of piano size
4) her registrations, worked by pedals, always included 16'.
She had, therefore, the triple octave range of 8, 4 and 16 foot. Her use of these were as follows: her standard norm for the harpsichord sonority was to maintain all the pedals pressed down, sounding simultaneously. When she wished a change of registration she lifted a pedal, that is, removed a registration — the opposite from the very nature of musical and registration applications of the harpsichord mechanism. I did not place an order for a harpsichord with Pleyel.
In performance, Landowska followed the nineteenth- and early twentieth-century style of transcription such as that of Liszt and Busoni, applying their style of adding octaves on the piano to the harpsichord, by a luxurious use of 16 foot and 4 foot; her applications simply reiterated their styles of octave additions in their Bach transcriptions for piano. Yet for the first part of this century, despite Sachs and others of the academic community, she was the most powerful influence as a performer in the representation of unassailable authenticity.
The harpsichords manufactured since the last thirty or so years have been modelled with increasing care in following manufacture instruction of earlier times. Do these modern replications produce the sounds that Bach heard from others and that he himself produced when playing the harpsichord? And do ourears hear the sounds of period instruments in the same way that musicians in the seventeenth and the first half of the eighteenth century perceived them? Does the late twentieth century stylistic manner of harpsichord and string playing (even with the curved bow) match, besides a few limited imitative elements, those of earlier times? Moreover, do human associations with pitch, sonority and timbre remain fixed throughout human history? Do our brains and our aural sense of pitch relationships identify with the varying tunings of the seventeenth and eighteenth centuries and do they cognize and, along with sensory responses, react to and interpret sound-structures and their relationships in the same way as did those of 300 years ago? In the last ten to twenty years the grave general doubts that have surfaced and spread in the academic community regarding our success in recreating the aesthetic concepts and performance manner of the past have given rise to similar questions. Such questions must continue to be asked, but in more detailed specificity in order to clear the assumptions and fuzziness that still cloud the near-universal, current historical approach.
There is no escaping our inherited aesthetic DNA pattern; we must face the effect upon us of our aesthetic parenthood and ancestry. The nineteenth century emphasised a focus on particularised textures and volumes as a result of the prolific development of orchestral and solo instruments. This focus nourished an attitude towards music that tied sonorities and timbres to first causes — in this case, the very structures of the music. The modern type of creative musicians, performers and listeners now think of all music, more often than not, in terms of specifically individualised sonorities. This view has its own history. Already in the second and third decades of the nineteenth century composers such as Berlioz revelled in colouristic orchestration, paving the way for Wagner in the development of clearly specified sonorities as representations of individualised character. The leitmotifs of Wagner serve as musical motifs that structure, identify and illuminate the dramatic as well as the musical characteristics. For the later tone painters, such as Debussy and Ravel, colour and texture assume major structural and representational functions. Depicting the picturesque is inherent in the very structures and instrumental allocations of such succeeding composers as Mussorgsky, Richard Strauss and early Stravinsky. Messiaen, Krenek, Boulez, Berio, to mention only very few twentieth century composers, far outstripped their predecessors in conceiving specific sonorities and volumes as indispensable structural elements. Such intrinsic structural functioning of sonorities and timbres is in actual fact a new musical use of sound; the simplistic, decorative and imitative sonority effects such as in early French music are alien to twentieth-century concepts of sound structuring. The music of contemporary composers forms an aural and conceptual background that supports and relates to the recreative, as well as the creative, musical expression of our epoch. These associations with specifically-allocated sonorities and timbres form the stamp of one of the most crucial identifying musical characteristics of our entire century.
 Bach, C. P. E., Essay on the True Art of Playing Keyboard Instruments, trans, and ed. by W.J. Mitchell, Eulenburg Books, London, 1974
 Op. cit. Marx, 
 One instance: in most universities, musicology and composition/performance are taught separately in different buildings.
 To mark the centenary of the foundation of the Halle Orchestra, I was engaged to perform Bach's Clavier Concerto BWV 1052, D minor, with the Halle Symphony Orchestra with Paul Hindemith as the conductor. He opened our rehearsal by saying to the orchestra, "Gentlemen, there are no dynamics in this concerto, therefore we play without dynamics."
 Sachs, C., The History of Musical Instruments, Norton, New York, 1940. Epilogue: The Twentieth Century, p 449.
 Dolmetsch A., The Interpretation of the Music of the XVIIth and XVIIIth Centuries, Novello, London, 1915.
 Sachs, op. cit. p. 450. "Many of our harpsichordists (but they are usually better than the gambists) play on modern reconstructions which, having pedals instead of less convenient hand stops, allow the lady to shift so rapidly from one combination to another that she occasionally indulges in the most astonishing coloristic excesses, to say nothing of her sixteen-foot debauches."
 These programs included the entire 48 Preludes and Fugues of the Well-Tempered Clavier, Suites, Partitas, Goldberg Variations and miscellaneous works.