The purpose of this paper is to discuss and to relate to each other two topics: (a) the admissibility of ignorance and mistake of fact as defences against negligence in crime; and (b) the inadmissibility of ignorance and mistake of law as defences against criminal charges. I am in (a) not concerned at all with torts negligence, only with criminal offences (whether common law or statutory) which can be committed negligently, where negligence suffices for liability, as in the law of homicide. This produces an untidy classification of elements, one or other of which is needed to provide the required mens rea (the exception of strict liability offences is here ignored): intention ( = purpose or aim), knowledge (or belief), recklessness and negligence. It is untidy, because the last does not belong on the same list as the other three, each of which can appropriately be called a state of mind in what we might say to be a positive sense, for each of them includes some degree of awareness of and/or attitude to relevant facts. If negligence is to be called (partly) a state of mind, it is so in a very stretched and negative way: to be told that a person was not attending to, thinking of or noticing something that he should have been is to be given some information, of a negative sort, about his state of mind, but it tells us very little, for it eliminates only one of an unlimited range of states of mind (in the positive sense). His not attending, noticing, etc., is equally compatible with his daydreaming (not attending to or noticing anything) and with his concentrating hard on something else. If negligence requires inadvertence, as is commonly maintained, then there was a state of mind which the agent should have been in but was not; if, as I would argue, it does not require inadvertence, then there was a state of mind which the agent should have been in, and maybe he was not in it, maybe he was in it. (In the present state of English law most offences of criminal negligence do require inadvertence, the notable exceptions being traffic offences such as careless driving. On the other hand, the proposal in the Law Commission Working Paper, No. 31 (1970) would not require it; the definition runs, ‘a person is negligent if he fails to exercise such care, skill or foresight as a reasonable man in his situation would exercise’. However, that is only a proposal; at present advertent negligence is rare in criminal law, although common in torts.) On this view, the questions are (1) whether his performance fell below scratch, (2) what are to be the excusing conditions for such a performance, and (3) if the answer to (1) is yes, whether his performance was covered by the excusing conditions.
