If the legislature seems to have purposefully left out a mental state element (mens rea) because they felt mental state need not be proven, it is treated as a strict liability. However, when a statute is silent as to the mental state (mens rea) and it is not clear that the legislature purposely left it out, the ordinary presumption is that a mental state is required for criminal liability. When no mens rea is specified, under the Model Penal Code (MPC), the default mens rea requirement is recklessness, which the MPC defines as "when a person consciously disregards a substantial and unjustifiable risk with respect to a material element".[11]