Pieter Bakker Key Characteristics
Het ORGEL 100 (2004), nr. 1, 33-37 [summary]

About a hundred years ago, German writers introduced the doctrine of the affections in musicology. The word affect had been used before, but it is not at all certain that it meant the same thing through the entire baroque period. Andreas Werckmeister, commonly considered the founder of the doctrine, distinguishes in fact just two musical affections: ‘Dur’ and ‘Moll’, joyous and sad. Werckmeister clearly prefers those temperaments that tend to pure fifths. In this respect he is influenced strongly by medieval theorists.
Johann Philipp Kirnberger was Considerably more modern. Although he promulgated three different classes of temperaments, which increased the range of affects considerably, he based these on the contemporary need to realise pure thirds – in reaction to Werckmeister’s striving to promote equal temperament. 
The discussion between Johann Mattheson and Johann Heinrich Buttstett in the early 18th century illustrates the shifts that took place with respect to ideas on key-character.