Let’s begin by examining what personal knowledge is. Consider someone that you know very well. You know a lot of facts about them this is factual knowledge. Some of these facts are shared with you only because you are trustworthy. For some of these facts, only long experience has revealed them to you. You also have theoretical knowledge of this person. You know that they are a human being. More specifically, you know that certain facts about them explain other facts. For example, you may be able to predict their desires well enough to get a present they like without asking them what they like. Finally, you have shared experiences with them, and those give knowledge of what they have done is particular situations. So this covers experiential, theoretical and factual knowledge. But there is no element of personal knowledge not covered by this sort of description. Therefore, personal knowledge is reducible to experiential, theoretical and factual knowledge.
Since personal knowledge is reducible to experiential, theoretical and factual knowledge, there is really no such thing distinct from them called personal knowledge. Personal knowledge is just the knowledge of a particular individual. We tend to think of this knowledge as being a kind of knowledge because this is the sort of knowledge gained through friendship with a particular person. But friendship is what unifies the knowledge of a person. Therefore, personal knowledge only seems like a distinct kind of thing because our friendship with a person is a distinct kind of thing.
I have shown that personal knowledge and practical knowledge can both be eliminated as distinct forms of knowledge. However, there may be further objections. First, someone may claim that these forms of knowledge are distinct forms of knowledge because they are unified by a common type of activity a skill or a friendship. Second, someone may claim that these may be distinct forms of knowledge that are just different from the common form of knowledge called factual knowledge.
Simply because a type of activity is the same does not mean that there is a distinct kind of knowledge required to do that activity. Creativity makes use of our understanding of the world (theoretical knowledge), but it a much different kind of activity than pure research. Nonetheless, both use theoretical knowledge. Furthermore, knowledge of medicine can be used to kill as well as to heal, but no one suggests that healing and killing are the same kind of activities! This shows that the same knowledge can appear in different activities. But killing does not require knowledge of medicine skill in using a bow would work just as well. Therefore, the same activity can make use of different kinds of knowledge.
Finally, we cannot simply suggest that there is a special kind of knowledge called ‘ personal knowledge’ unless there is some kind of connection to other forms of knowledge. Otherwise we would simply be using ‘knowledge’ equivocally and one of the things called ‘ knowledge’ would not really be knowledge at all.