The Gettier Problem

In Plato’s Theaetetus, we are asked to consider the difference between knowledge and mere opinion. Knowledge, we learn, must be about something that is true. While you might have a false opinion, you cannot be said to properly know something when it’s false. And drawing from imagery in the Meno, we might add that knowledge is “tied down” in a way that a mere opinion is not—if you know that p then you have reason or justification for believing p. Mere opinions are fragile in a way that knowledge is not. Mere opinions might be swayed via rhetoric or persuasion. Knowledge, it’s thought, is gained via education and is far less fragile. In sum, then, mere opinions are beliefs that are supported by little or at least insufficient justification and may or may not be true. And knowledge, in contrast, is a belief that is true and sufficiently justified. Belief, sufficient justification, and truth were considered, since time immemorial (or so the story goes), to be necessary conditions on knowledge. In his seminal 1963 article, “Is Justified True Belief Knowledge?,” Edmund Gettier argued that, while justification, truth, and belief may be necessary for knowledge, such conditions are not (when taken together) sufficient for knowledge. In other words, Gettier argued that a belief could be justified and true and yet fail to be an instance of knowledge.