  In a recent article, Dieks has proposed a way to implement the modal
interpretation of (nonrelativistic) quantum theory in relativistic quantum
field theory. We show that his proposal fails to yield a well-defined
prescription for which observables in a local spacetime region possess definite
values. On the other hand, we demonstrate that there is a well-defined and
unique way of extending the modal interpretation to the local algebras of
relativistic quantum field theory. This extension, however, faces a potentially
serious difficulty in connection with ergodic states of a field.
