This research examined the ability of three-and-four-year-olds to use domains of knowledge to evaluate sources of knowledge. Participants were presented with a causal expert who fixed broken toys and a verbal expert who knew the names of tools. Participants were then asked if they should ask the causal expert or verbal expert for assistance with two questions each concerning causal, verbal, and functional knowledge. Four-year-olds, but not three-year-olds, selected to ask the causal expert for causal knowledge and the verbal expert for verbal knowledge. In terms of functional knowledge, as a group participants did not prefer one expert over another. However, four-year-olds selected the same expert for both functional questions at a significant level, suggesting they had a firm decision about which expert was best suited to answer the functional questions. These results suggest four-year-olds are able to use domains of knowledge to evaluate the epistemic states of other people and have theories about how verbal, functional, and causal knowledge relate to one another.