Process reliabilism has been used as an argument against philosophical skepticism, such as the brain in a vat thought experiment.
Since Gettier[2] proposed his counterexamples the traditional analysis has included the further claim that knowledge must be more than justified true belief.
On this view, those who offer reliabilist theories of justification further analyze the 'justification' part of the traditional analysis of 'knowledge' in terms of reliable processes.
In defending this view, reliabilists (and externalists generally) are apt to point to examples from simple acts of perception: if one sees a bird in the tree outside one's window and thereby gains the belief that there is a bird in that tree, one might not at all understand the cognitive processes that account for one's successful act of perception; nevertheless, it is the fact that the processes worked reliably that accounts for why one's belief is justified.
Reliabilism usually considers that for generating justified beliefs a process needs to be reliable in a set of relevant possible scenarios.
Brandom is concerned that unless the role of belief is stressed, reliabilism may attribute knowledge to things that would otherwise be considered incapable of possessing it.
The proposition is true, the mechanism that produced it is reliable, but Brandom is reluctant to say that the parrot knows it is seeing red because he thinks it cannot believe that it is.