Cassam (Self-Knowledge for humans. Oxford University Press, 2014) introduced the term substantial self-knowledge to capture self-knowledge that is difficult to attain and plays a central role in one’s life and self-conception. Knowing whether one wants another child, whether one is a kind person, or whether one values honesty are unlike many trivial cases of knowing one’s occurrent mental state, such as knowing that one is in pain or believes it is 10 am. In response to the difficulty of substantial self-knowledge agents can and already do use external objects to gain such self-knowledge. I present a series of cases of tool-assisted self-knowledge and argue that while often not recognised as such, this form of self-knowledge is commonplace. I suggest that it is best understood as a form of self-knowledge that is inferred from evidence. I explain how external objects can be a part of that inferential process along three dimensions: the generation of evidence, the tracking of evidence, and the performance of the inference that leads to self-knowledge. I provide a rough taxonomy based on these dimensions as a framework for further research.
