This rival theory begins with the claim that justification is distinct from argument and reasoning. All beliefs may be justified by their relation to others by mutual support. Analogously, justification is based on agreement with a system of beliefs. Coherentism is given a full airing in Chapter 5 and Chapter 6 . The right sort of connection between belief and reality yields knowledge.
Causality is one contender.
Justification may not even be needed. Externalism is treated in Chapter 8 . Lehrer indicates here that both the foundationalist and the coherentist think the externalist is wrong to allow the possibility that a person may know without having any idea how belief and reality are connected in the case in question. The engine of the system to be adopted here will be coherentist. Coherence in what a person accepts is a subjective fact about that person, so the the coherence theory to be given will to some extent be subjetive.