Group Knowledge and Epistemic Defeat

If individual knowledge and justification can be vanquished by epistemic defeaters, then the same should go for group knowledge. Lackey (2014) has recently argued that one especially strong conception of group knowledge defended by Bird (2010) is incapable of explaining how it is that (group) knowledge is ever subject to ordinary mechanisms of epistemic defeat. Lackey takes it that her objections do not also apply to a more moderate articulation of group knowledge—one that is embraced widely in collective epistemology—and which she does not challenge. This paper argues that given certain background premises that are embraced by orthodox thinking in collective epistemology, the more moderate account of group knowledge cannot make sense of either psychological or normative epistemic defeaters. I conclude by offering some suggestions for how the more moderate proposal might avoid this result.