The public have an interest in every person's carrying on his trade freely: so has the individual. All interference with individual liberty of action in trading, and all restraints of trade of themselves, if there is nothing more, are contrary to public policy, and therefore void. That is the general rule. But there are exceptions: restraints of trade and interference with individual liberty of action may be justified by the special circumstances of a particular case.
It is a sufficient justification, and indeed it is the only justification, if the restriction is reasonable — reasonable, that is, in reference to the interests of the parties concerned and reasonable in reference to the interests of the public, so framed and so guarded as to afford adequate protection to the party in whose favour it is imposed, while at the same time it is in no way injurious to the public. That, I think, is the fair result of all the authorities.