What Is Expertise?

Nowadays, we have to rely on experts in many theoretical and practical matters. We consider them reliable and rely on them. To justify many of our beliefs, we have no other reason but the testimony of experts. Nonetheless, to trust the experts, it is necessary to recognize them and know their distinctive characteristics. In doing so, epistemologists proposed some definitions for experts and expertise. In this paper, First, we will explain the truth-based definition and then the justification-based definition and describe the criticisms of it. we show that the best definition is that S is an expert in domain D if and only if S has more understanding and ability than most people in domain D at his time. In the end At the end, we explain the five necessary conditions of belief, coherence, ability, efficiency and time.