Full Idea
The 'Relevant Alternatives' theory of knowledge said the main ingredient that must be added to true belief to make knowledge is that one be in a position to rule out all the relevant alternatives to what one believes.
Gist of Idea
You have knowledge if you can rule out all the relevant alternatives to what you believe
Source
report of Fred Dretske (Epistemic Operators [1970]) by Keith DeRose - Intro: Responding to Skepticism §6
Book Reference
'Skepticism', ed/tr. DeRose,K /Warfield,Ted [OUP 1999], p.14
A Reaction
Dretske and Nozick are associated with this strategy. There will obviously be a problem in defining 'relevant'. Otherwise it sounds quite close to Plato's suggestion that we need true belief with 'logos'.