  We propose a definition of determinism for a physical system that includes,
besides the measurement device, the surrounding environment. This enlarged
system is assumed to follow a predefined trajectory starting from some
(unknown) initial conditions that play the role of hidden variables for the
experiment. These assumptions, which are different from realism, allow us to
derive a type of time Bell inequalities, which are violated by Quantum
Mechanics. In order to illustrate this violation, we discuss the particular
case of measurements on a spin 1/2 particle.
