The 6 Trios by J S. Bach, as originally described in the surviving manuscript bears the name of neither the arranger of Bach’s pieces nor the composer of the slow introductions. Despite that, it has long been supposed that it was the work of W. A. Mozart. As far as we can trace, it was Wilhelm Rust, the editor of the volume 9 of the Bach-Gesellschaft edition, who in 1860 first made this connection. A more recent scholarship has identified many details that help us understand the complex backgrounds of these textual deviations found in the surviving manuscripts originated from Vienna in 1770-1800. Each Trio consists of a slow introduction and a fugue. While it retains Bach’s original prelude-fugue design, the keyboard prelude was replaced with something more suitable for string ensemble. In a sense, the arrangement has a close affiliation with the Baroque Sonata da chiesa (i.e. the first two movements of the four-movement set "slow-fast-slow-fast"), the genre, which represents the repertoire of the past, appears to have been much appreciated among the connoisseurs of music in the late eighteenth-century Vienna. The slow introduction typically begins in the tonic and closes in the dominant, so that the main piece, the fugue, can begin in a well-prepared mood. Similarly it makes use of the melodic material that hints the ensuing announcement of the fugue subject. Thus the introduction unfolds in such a manner so that when the fugue subject appears ceremoniously, one feels that at last a show has begun