justified knowledge

I've been reading chapter 4 and I'm understanding the discussion, but I'm not sure what perspective Elgin is taking. I'm thinking she is somehow rejecting the idea that we must individually justify everything we "know." I got that from the part where she says that if we were only to believe what we individually who justify then how could I possibly believe water is, in fact, H2O since I did not take part in deciding/"proving" that. I like this idea because it means we are allowed to trust others in doing some of the justification for us. However, I would like to know her thoughts on how we should decide whom we can use for justification purposes and how we should decide this. I'm assuming she'll present this idea in the rest of the chapter, but I'm not gonna lie, sometimes I read stuff and totally miss the point, so we should discuss this next week.