Another crime in which the peculiarities noticed in larceny are still more clearly marked, and at the same time more easily explained, is burglary. It is defined as breaking and entering any dwelling-house by night with intent to commit a felony therein. /2/ The object of punishing such a breaking and entering is not to prevent trespasses, even when committed by night, but only such trespasses as are the first step to wrongs of a greater magnitude, like robbery or murder. /3/ In this case the function of intent when proved appears more clearly than in theft, but it is precisely similar. It is an index to the probability of certain future acts which the law seeks to prevent. And here the law gives evidence that this is the true explanation. For if the apprehended act did follow, then it is no longer necessary to allege that the breaking and entering was with that intent. An indictment for burglary which charges that [75] the defendant broke into a dwelling-house and stole certain property, is just as good as one which alleges that he broke in with intent to steal. /1/ It is believed that enough has now been said to explain the general theory of criminal liability, as it stands at common law. The result may be summed up as follows. All acts are indifferent per se. In the characteristic type of substantive crime acts are rendered criminal because they are done finder circumstances in which they will probably cause some harm which the law seeks to prevent. The test of criminality in such cases is the degree of danger shown by experience to attend that act under those circumstances. In such cases the mens rea, or actual wickedness of the party, is wholly unnecessary, and all reference to the state of his consciousness is misleading if it means anything more than that the circumstances in connection with which the tendency of his act is judged are the circumstances known to him. Even the requirement of knowledge is subject to certain limitations. A man must find out at his peril things which a reasonable and prudent man would have inferred from the things actually known. In some cases, especially of statutory crimes, he must go even further, and, when he knows certain facts, must find out at his peril whether the other facts are present which would make the act criminal. A man who abducts a girl from her parents in England must find out at his peril whether she is under sixteen.