The test for the existence of mens rea may be:(a) subjective, where the court must be satisfied that the accused actually had the requisite mental element present in his or her mind at the relevant time (for purposely, knowingly, recklessly etc) (see concurrence);(b) objective, where the requisite mens rea element is imputed to the accused, on the basis that a reasonable person would have had the mental element in the same circumstances (for negligence); or(c) hybrid, where the test is both subjective and objective.
The court will have little difficulty in establishing mens rea if there is actual evidence – for instance, if the accused made an admissible admission. This would satisfy a subjective test. But a significant proportion of those accused of crimes makes no such admission. Hence, some degree of objectivity must be brought to bear as the basis upon which to impute the necessary components. It is always reasonable to assume that people of ordinary intelligence are aware of their physical surroundings and of the ordinary laws of cause and effect (see causation). Thus, when a person plans what to do and what not to do, he will understand the range of likely outcomes from given behaviour on a sliding scale from “inevitable” to “probable” to “possible” to “improbable”. The more an outcome shades towards the “inevitable” end of the scale, the more likely it is that the accused both foresaw and desired it, and, therefore, the safer it is to impute intention. If there is clear subjective evidence that the accused did not have foresight, but a reasonable person would have, the hybrid test may find criminal negligence. In terms of the burden of proof, the requirement is that a jury must have a high degree of certainty before convicting, defined as “beyond a reasonable doubt” in the United States and “sure” in the United Kingdom. It is this reasoning that justifies the defenses of infancy, and of lack of mental capacity under the M’Naghten Rules, an alternate common law rule (e.g., Durham rule), and one of various statutes defining mental illness as an excuse. Moreover, if there is an irrebuttable presumption of doli incapax – that is, that the accused did not have sufficient understanding of the nature and quality of his actions – then the requisite mens rea is absent no matter what degree of probability might otherwise have been present. For these purposes, therefore, where the relevant statutes are silent and it is for the common law to form the basis of potential liability, the reasonable person must be endowed with the same intellectual and physical qualities as the accused, and the test must be whether an accused with these specific attributes would have had the requisite foresight and desire.
In English law, s8 Criminal Justice Act 1967 provides a statutory framework within which mens rea is assessed. It states:A court or jury, in determining whether a person has committed an offense,(a) shall not be bound in law to infer that he intended or foresaw a result of his actions by reasons only of its being a natural and probable consequence of those actions; but(b) shall decide whether he did intend or foresee that result by reference to all the evidence, drawing such inferences from the evidence as appear proper in the circumstances.
Under s8(b) therefore, the jury is allowed a wide latitude in applying a hybrid test to impute intention or foresight (for the purposes of recklessness) on the basis of all the evidence.