Full Idea
The first to link the art forms together explicitly and to separate them from other disciplines and activities were the authors of encyclopedias and books in the 1740s and 1750s.
Gist of Idea
The idea that art forms are linked into a single concept began in the 1740s
Source
Stephen Davies (The Philosophy of Art (2nd ed) [2016], 1.2)
Book Reference
Davies,Stephen: 'The Philosophy of Art (2nd ed)' [Wiley Blackwell 2016], p.6
A Reaction
Intriguing that no individual seems to get the credit (or blame). Presumably our modern Aesthetics (applied to art) couldn't exist before this move was made - and yet there is plenty of aesthetic discussion in early Greek philosophy.