IGNORANCE, or mistake, in Law, a defect of will, by which a person is excused from the guilt of a crime, when, intending to do a lawful act, he does that which is unlawful. For here the deed and the will acting separately, there is not that conjunction between them which is necessary to constitute a criminal act. But this must be an ignorance or mistake of fact, and not an error in point of law. For a mistake in point of law, which every person of discretion not only may, but is bound and presumed to know, is, in criminal cases, no sort of defence. Ignorantia juris, quod quisque tenetur scire, neminem excusat, is as well the maxim of our own law as it was of the Roman.