 To state conditions that are jointly sufficient for knowledge, what further element must be added to JTB? This is known as the Gettier problem. Some philosophers attempt to solve the Gettier problem by adding a fourth condition to the three conditions mentioned above, while others attempt to solve it by either replacing or refining the justification condition. How we understand the contrast between replacing the justification condition and refining it depends, of course, on how we understand the justification condition itself, which is the topic of the next section.