The principle which he deduces from these considerations is--'that the sole end for which mankind are warranted, individually or collectively, in interfering with the liberty of action of any of their number is self-protection; the only purpose for which power can be rightfully exercised over any member of a civilised community, is to prevent harm to others. His own good, either physical or moral, is not a sufficient warrant. He cannot be rightfully compelled to do or forbear because it will make him happier, because in the opinion of others to do so would be wise or even right. These are good reasons for remonstrating with him, or reasoning with him, or persuading him, or entreating him, but not for compelling him, or visiting him with any evil in case he do otherwise. To justify that, the conduct from which it is desired to deter him must be calculated to produce evil to others.' (_Liberty_, 22.) Two disputable points in the above doctrine are likely at once to reveal themselves to the least critical eye. First, that doctrine would seem to check the free expression of disapproval; one of the most wholesome and indispensable duties which anybody with interest in serious questions has to perform, and the non-performance of which would remove the most proper and natural penalty from frivolous or perverse opinions and obnoxious conduct. Mr. Mill deals with this difficulty as follows:--'We have a right in various ways to act upon our unfavourable opinion of any one, not to the oppression of his individuality, but in the exercise of ours. We are not bound, for example, to seek his society; we have a right to avoid it (though not to parade the avoidance) for we have a right to choose the society most acceptable to us. We have a right, and it may be our duty, to caution others against him, if we think his example or conversation likely to have a pernicious effect on those with whom he associates. We may give others a preference over him in optional good offices, except those which tend to his improvement. In these various modes a person may suffer very severe penalties at the hands of others for faults which directly concern only himself; but he suffers these penalties only in so far as they are the natural, and as it were the spontaneous, consequences of the faults themselves, not because they are purposely inflicted on him for the sake of punishment.' (_Liberty_, 139.) This appears to be a satisfactory way of meeting the objection. For though the penalties of disapproval may be just the same, whether deliberately inflicted, or naturally and spontaneously falling on the object of such disapproval, yet there is a very intelligible difference between the two processes in their effect on the two parties concerned. A person imbued with Mr. Mill's principle would feel the responsibility of censorship much more seriously; would reflect more carefully and candidly about the conduct or opinion of which he thought ill; would be