Full Idea
Until the rise of what we call the scientific method in the seventeenth century, logic was regarded largely as one aspect of rhetoric - a study of how one person't argument could convince another.
Gist of Idea
Logic was merely a branch of rhetoric until the scientific 17th century
Source
Keith Devlin (Goodbye Descartes [1997], Ch.11)
Book Reference
Devlin,Keith: 'Goodbye Descartes: the end of logic' [Wiley 1997], p.261
A Reaction
This may well give the main reason why the Greeks invented logic in the first place. Aristotle wrote a book on rhetoric, and that was where the money was. Leibniz is clearly a key figure in the change of attitude.