The philosophical study of knowledge asks profound questions:
What is knowledge?
What is required for knowledge?
What is the extent of our knowledge?
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):
P is true.
S believes P.
If P were not true, S would not believe P.
If P were true, S would believe 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.