I quote again on this subject from Mr. Bishop: "The doctrine of _the intent_ as it prevails in the criminal law, is necessarily _one of the foundation principles of public justice_. There is only one criterion by which the guilt of man is to be tested. It is whether the mind is criminal. Criminal law relates only to crime. And neither in philosophical speculation, nor in religious or moral sentiment, would any people in any age allow that a man should be deemed guilty unless his mind was so. It is, therefore, a principle of our legal system, as probably it is of every other, that _the essence of an offence is the wrongful intent without which it cannot exist_." (_1 Bishop's Crim. Law, Sec.287._) Again, the same author, writing on the subject of _knowledge_, as necessary to establish the intent, says: "It is absolutely necessary to constitute guilt, as in indictments for uttering forged tokens, or other attempts to defraud, or for receiving stolen goods, and offences of a similar description." (_1 Crim. Prac. Sec.504._) In regard to the offence of obtaining property by false pretenses, the author says: "The indictment must allege that the defendant knew the pretenses to be false. _This is necessary upon the general principles of the law_, in order to show an offence, even though the statute does not contain the word 'knowingly.'" (_2 Id. Sec.172._) As to a _presumed knowledge_ of the law, where the fact involves a question of law, the same author says: "The general doctrine laid down in the foregoing sections," (i.e. that every man is presumed to know the law, and that ignorance of the law does not excuse,) "is plain in itself and plain in its application. Still there are cases, the precise nature and extent of which are not so obvious, wherein ignorance of the law constitutes, in a sort of indirect way, not in itself a defence, but a foundation on which another defence rests. Thus, if the guilt or innocence of a prisoner, depends on the fact to be found by the jury, of his having been or not, when he did the act, in some precise mental condition, _which mental condition is the gist of the offence_, the jury in determining this question of mental condition, _may_ take into consideration his ignorance or misinformation in a matter of law. For example, to constitute larceny, there must be an intent to steal, which involves the knowledge that the property taken does not belong to the taker; yet, if all the facts concerning the title are known to the accused, and so the question is one merely of law whether the property is his or not, still he may show, and the showing _will be a defence_ to him against the criminal proceeding, that he _honestly believed it his through a misapprehension of the law_." (1 Cr. Law, Sec.297.)