Free Trade, so neither is it in most of the questions which arise respecting the limits of that doctrine: as for example, what amount of public control is admissible for the prevention of fraud by adulteration; how far sanitary precautions, or arrangements to protect work-people employed in dangerous occupations, should be enforced on employers. Such questions involve considerations of liberty, only in so far as leaving people to themselves is always better, caeteris paribus , than controlling them: but that they may be legitimately controlled for these ends, is in principle undeniable. On the other hand, there are questions relating to interference with trade, which are essentially questions of liberty; such as the Maine Law, already touched upon; the prohibition of the importation of opium into China; the restriction of the sale of poisons; all cases, in short, where the object of the interference is to make it impossible or difficult to obtain a particular commodity. These interferences are objectionable, not as infringements on the liberty of the producer or seller, but on that of the buyer.
One of these examples, that of the sale of poisons, opens a new question; the proper limits of what may be called the functions of police; how far liberty may legitimately be invaded for the prevention of crime, or of accident. It is one of the undisputed functions of government to take precautions against crime before it has been committed, as well as to detect and punish it afterwards. The preventive function of government, however, is far more liable to be abused, to the prejudice of liberty, than the punitory function; for there is hardly any part of the legitimate freedom of action of a human being which would not admit of being represented, and fairly too, as increasing the facilities for some form or other of delinquency. Nevertheless, if a public authority, or even a private person, sees anyone evidently preparing to commit a crime, they are not bound to look on inactive until the crime is committed, but may interfere to prevent it. If poisons were never bought or used for any purpose except the commission of murder, it would be right to prohibit their manufacture and sale. They may, however, be wanted not only for