Much of what we know is based on the evidence of testimony, rather than the evidence of our senses. Consider your knowledge of your birthday. Your evidence that you were born on a particular date is based on information from your parents, your birth certificate, and other testimonial evidence. You were there, of course, and you were sensing. But the sensory information you had at the time did not count as evidence. Your knowledge of your birth is a bit of empirical knowledge, as are other items of historical knowledge. Indeed, a great percentage of your beliefs are based on the testimony of others. Your excellent question about whether testimony is “subsumed by empirical knowledge” might be understood as the question of whether testimonial knowledge can be reduced to some more basic kind of empirical knowledge, such as sensory-based knowledge. This is a controversial issue in the epistemology of testimony. Some beliefs that are justified by testimony can be independently checked by first-person...

You've nicely articulated several of the fundamental questions in the philosophy of mind and epistemology - the problem of other minds and the problem of the external world. If your knowledge of the world is gained through awareness of your own thoughts, how do you know that there are other thinking persons, and indeed how do you know that there is a world external to your thoughts, a world of other persons and physical objects? The question of whether what philosophers call solipsism , that you, as a thinking thing, might be the sole existing entity is possible, is at the heart of discussions of this issue, both in historical philosophical texts and in contemporary discussions. In his Meditations on First Philosophy , Rene Descartes provides arguments for solipsism in the early part of his work, but then attempts to show that we prove the existence of a wholly good god who would not deceive us about our ordinary beliefs about the existence of other persons and the external world. As Charles...

The fact thatyou're talking about Descartes and the cogito witha friend is an excellent start. It is certainly a main part of theproject of Descartes' Meditations on First Philosophy to prove that one can have knowledge of a world which extends beyondone's awareness of oneself as a thinking thing. I would recommend acareful reading of that work, with particular attention to the thirdMeditation, where Descartes explicitly considers and rejects thesuggestion you've hinted at, namely that the existence of a worldoutside oneself follows from the fact that the world seems to imposeitself on us, often against our will. Descartes rejects this argumentbecause it is possible that such ideas could still be invented by us,and only appear to issue from outside us. This point is made inpreparation for the proof of God's existence in Meditation 3, whereDescartes argues that when one reflects on the content of one's mind,only our possession of the idea of God requires that there...

Thetraditional account of knowledge is that truth is one of three necessaryconditions for knowledge. The other two are belief and justification. On thisaccount, if X knows that p, then (1) X believes that p, (2) X is justified inbelieving p, and (3) p is true. Thus if a widely held justified beliefturned out to be false, then the belief would not count as knowledge. Of course there is much work to be done inspelling out what we are to understand by belief, justification, and truth. A great deal ofattention to this definition and the question of its adequacy followed EdmundGettier’s paper “Is Justified True Belief Knowledge?” ( Analysis 23 ( 1963): 121-123; available online at http://www.ditext.com/gettier/gettier.html )