Full Idea
Most defeasible reasoning is externally dynamic, affected by the addition of further premises. But there is also an internal (or 'diachronic') dynamic, when further analysis reveals more about the given premises.
Gist of Idea
Reasoning may be defeated by new premises, or by finding out more about the given ones
Source
G. Aldo Antonelli (Non-Monotonic Logic [2014], 1)
Book Reference
'Stanford Online Encyclopaedia of Philosophy', ed/tr. Stanford University [plato.stanford.edu], p.2