On the other hand, there can be no case in which the law-maker makes certain conduct criminal without his thereby showing a wish and purpose to prevent that conduct.  Prevention would accordingly seem to be the chief and only universal purpose of punishment.  The law threatens certain pains if you do certain things, intending thereby to give you a new motive for not doing them.  If you persist in doing them, it has to inflict the pains in order that its threats may continue to be believed.

If this is a true account of the law as it stands, the law does undoubtedly treat the individual as a means to an [47] end, and uses him as a tool to increase the general welfare at his own expense.  It has been suggested above, that this course is perfectly proper; but even if it is wrong, our criminal law follows it, and the theory of our criminal law must be shaped accordingly.

Further evidence that our law exceeds the limits of retribution, and subordinates consideration of the individual to that of the public well-being, will be found in some doctrines which cannot be satisfactorily explained on any other ground.

The first of these is, that even the deliberate taking of life will not be punished when it is the only way of saving one’s own.  This principle is not so clearly established as that next to be mentioned; but it has the support of very great authority. 1 If that is the law, it must go on one of two grounds, either that self-preference is proper in the case supposed, or that, even if it is improper, the law cannot prevent it by punishment, because a threat of death at some future time can never be a sufficiently powerful motive to make a man choose death now in order to avoid the threat.  If the former ground is adopted, it admits that a single person may sacrifice another to himself, and a fortiori that a people may.  If the latter view is taken, by abandoning punishment when it can no longer be expected to prevent an act, the law abandons the retributive and adopts the preventive theory.

The next doctrine leads to still clearer conclusions.  Ignorance of the law is no excuse for breaking it.  This substantive principle is sometimes put in the form of a rule of evidence, that every one is presumed to know the [48] law.  It has accordingly been defended by Austin and others, on the ground of difficulty of proof.  If justice requires the fact to be ascertained, the difficulty of doing so is no ground for refusing to try.  But every one must feel that ignorance of the law could never be admitted as an excuse, even if the fact could be proved by sight and hearing in every case.  Furthermore, now that parties can testify, it may be doubted whether a man’s knowledge of the law is any harder to investigate than many questions which are gone into.  The difficulty, such as it is, would be met by throwing the burden of proving ignorance on the lawbreaker.

The principle cannot be explained by saying that we are not only commanded to abstain from certain acts, but also to find out that we are commanded.  For if there were such a second command, it is very clear that the guilt of failing to obey it would bear no proportion to that of disobeying the principal command if known, yet the failure to know would receive the same punishment as the failure to obey the principal law.