Authorship of this Sonata is doubtful. The composer is given only as "Sign Pagh". J.M. Bach has been suggested as the most likely composer.
||Sonata à 4 in G minor
RISM lists 3 violas, but the 3rd viola part is the basso part.
(Viola doesn't necessarily mean "alto viola da braccio" until late in the 18th century. Viola just means "string instrument", so a continuo part could be played by a "viola di basso", "Viola da brazzo", "violon" or "violone" (a bass violin, bass viol or G-violone [with or without the deep G]) and the the two upper viola parts could be played by any suitable size of "viola da gamba" or "viola da braccio". The "violino" is just a diminutive of "viola", so any small string instrument could be meant, for instance a treble viol, a pardessus de viole, a violin or a viola d'amoure. Interpreting terms from the past as if they meant the same as today usually leads to confusion.)