Full Idea
Modus ponens is just one of the five different inference rules identified by the Stoics.
Clarification
'Modus ponens' says if p implies q, and p is true, then q must be true
Gist of Idea
Modus ponens is one of five inference rules identified by the Stoics
Source
report of Chrysippus (fragments/reports [c.240 BCE]) by Keith Devlin - Goodbye Descartes Ch.2
Book Reference
Devlin,Keith: 'Goodbye Descartes: the end of logic' [Wiley 1997], p.36
A Reaction
Modus ponens strikes me as being more like a definition of implication than a 'rule'. Implication is what gets you from one truth to another. All the implications of a truth must also be true.