Full Idea
If externalism is the final story, we have no reason to think that any of our beliefs are true, which amounts to a very strong and intuitively implausible version of scepticism.
Gist of Idea
Externalism means we have no reason to believe, which is strong scepticism
Source
Laurence Bonjour (In Defence of Pure Reason [1998], §3.7)
Book Reference
Bonjour,Laurence: 'In Defense of Pure Reason' [CUP 1998], p.96
A Reaction
A very good point. I may, like a cat, know many things, with good external support, but as soon as I ask sceptical questions, I sink without trace if I lack internal reasons.