Full Idea
Pure coherentists claim that a belief can only be justified by its relations to other beliefs; impure coherentists are willing to give some non-beliefs, such as perceptual experiences, a justifying role.
Gist of Idea
Impure coherentists accept that perceptions can justify, unlike pure coherentists
Source
James Pryor (There is immediate Justification [2005], §4)
Book Reference
'Contemporary Debates in Epistemology', ed/tr. Steup,M/Sosa,E [Blackwell 2005], p.185
A Reaction
I think I would vote for the pure version. The distinction that is needed, I think, is between justification and evidence. You have to surmise causal links and explanations before you can see an experience as evidence, and then justification.