The philosophical study of knowledge asks profound questions:

Justified true beliefs can be problematic: Imagine a woman who pops pills that cause irrational fears. She worries that she has cancer, then she believes it. Coincidentally, she develops cancer. Her belief now holds true, but her knowledge is not justified. To know that she has cancer, the woman must be diagnosed.

To solve this problem, Robert Nozick reasoned that knowledge has four conditions. For a subject (S) to know a proposition (P):

Debates between atheists and non-atheists hinge on criteria for truth. Many atheists require empirical evidence to establish the truth of a proposition: they dismiss coincidence as evidence.