A good pointer to the EPR-problem is the Wikipedia entry. The article contains links to download
- the original paper of Einstein, Podolsky and Rosen
- the reply of Bohr in the same journal
- a corresponding entry in Stanford Encyclopedia of Philosophy
You find even more references in the article, in particular to Bell's papers. I recommend also "Andrew Whitaker: Einstein, Bohr and the Quantum Dilemma. Cambridge (1996)", Ch. 6 and 7.
Added after reading the EPR-paper: The EPR-paper starts with two useful statements which link physics and natural philosophy:
Physical reality: „If, without in any way disturbing a system, we can predict with certainty […] the value of a physical quantity, then there exists an element of physical reality corresponding to this physical quantity.“
Complete theory: „[…] the following requirement für a complete theory seems to be a necessary one: every element of the physical reality must have a counterpart in the physical theory.“
The problematic term from natural philosophy is the term „physical reality“.
The authors do not define the term, their second statement does not fix the kind of relation between the physical quantity from the theory and the corresponding element of physical reality.
Their first statement requires the existence of a map from a certain subset of physical quantities of the theory to the set of elements of physical reality.
While their second statement goes the other way round. It requires for a complete theory the existence of a map from the set of all elements of physical reality to a certain subset of physical quantities of the theory.