Full Idea
If you don't know which letters belong together in the right syllables…it is possible for true belief to be accompanied by a rational account and still not be entitled to the name of knowledge.
Gist of Idea
An inadequate rational account would still not justify knowledge
Source
Plato (Theaetetus [c.364 BCE], 208b)
Book Reference
Plato: 'Theaetetus', ed/tr. Waterfield,Robin [Penguin 1987], p.126
A Reaction
In each case of justification there is a 'clinching' stage, for which there is never going to be a strict rule. It might be foundational, but equally it might be massive coherence, or no alternative.