To discuss the role of tacit knowledge in expertise we must first clarify what expertise and tacit knowledge mean. In our discussion we all agreed to the definition given in the MITECS paper that "Expertise refers to the mechanisms underlying the superior achievement of an expert". Some important features of this statement must be noted. Firstly, the phrase "superior achievement" is a comparative phrase and demands defining of a particular field. Secondly, the definition does not say anything about an expert. Now according to our view the exact idea of the superior achievement, in itself manifests the meaning of word "Expert" and the idea being that the achievement that is being concerned must have a greater social recognition than the achievement of a person that is not considered as an expert. Thus from this idea the two features that we concluded to be necessarily possessed by a person to call himself an expert in a particular field are:
1. He must have acquired special skill in a particular field or knowledge of a particular subject. (Ericssion et. al)
2. He must be able to produce results of greater social recognition in that particular field.
Having defined an expert explicitly, the next question that arises is: How an expert acquires this special set of skills and how is he different from a person having the same skills but not being considered as an expert? In the MITECS paper it is mentioned that these skills are acquired through particular experience but the study about the distinguishing features of an expert shows that expert did not differ in the speed of their thoughts or the size of their basic memory capacity, and their ability to recognize promising potential techniques but expert performance is viewed as an extreme case of skill acquisition (Proctor and Dutta 1995; Richman et al. 1996; VanLehn 1996) and as the final result of the gradual improvement of performance during extended experience in a domain. Now we believe what happens in this period of extended exposure to the field of expertise involves tacit knowledge.
Wikipedia defines Tacit knowledge as the kind of knowledge that is difficult to transfer to another person by means of writing it down or verbalising it. Another term for it is implicit knowledge which means the information which does not involves conscious efforts for retrieval. In his essay "Implicit learning and Tacit knowledge" Arthur S Reber describes many experiments not only proves the existence of such a technique of knowledge acquisition and memory but also brings to light the fact that such a memory or knowledge is far more stronger and dominant the conscious knowledge.
What we think is that when a person is exposed to a training procedure or various situations in a particular field the information about the situation is not only being consciously analysed but also being stored and analysed implicitly. Now when the person is again exposed to the same field this implicit knowledge help him percept the situation more efficiently and in a manner that is more easy and proficient than the person exposed to the situation for the first time. Such extended exposures result in the formation of a vast repository of implicit knowledge which in turn makes a makes an expert. The fact that the domain of expertise is limited and cannot be translated to other domains can be explained by assuming that the exposures were restricted to a particular field and hence the repository pertains to that field only.
Thus, we conclude that Tacit or Implicit knowledge is the very basis of expertise.