When i was playing this prelude from bach i came across a new chord that i don't usually see in 18th century pieces Also another question - in writing counterpoint in bach style it looks like two eight notes in a row can be dissonance without resolving is this true ? ( as i mentiond the interval between bass and alto with 2 and 7 )
Harmonically this is F♯m7, and the G♯ is a passing note. It is important to keep in mind that Bach did not really use Rameau style harmony theory, neither did he write Renaissance style counter point. The important thing here is that contrary to a suspension where the dissonance falls on a heavy beat and needs to be resolved the dissonance falls on a weak beat and does not resolve. This is not particularly uncommon, and there are quite a few cases of spicy harmonics going on in the work of Bach and other composers around that time.
