  We define a new construct in quantum field theory - the causal density matrix
- obtained from the singularity structure of correlators of local operators.
This object provides a necessary and sufficient condition for a quantum field
theory state to have a holographic semiclassical dual causal geometry. By
exploiting the causal density matrix, we find that these dual causal geometries
quite generally (even away from AdS/CFT) exhibit features of quantum error
correction. Within AdS/CFT, we argue that the "reduced" causal density matrix
is the natural dual to the causal wedge. Our formalism is very well-suited to
generalizations of holography beyond AdS/CFT or even gravity/QFT.
