"The maxims are, first, that the individual is not accountable to society for his actions, in so far as these concern the interests of no person but himself...Secondly, that for such actions as are prejudicial to the interests of others, the individual is accountable, and may be subjected either to social or legal punishments, if society is of opinion that the one (social punishment) or the other (legal punishment) is requisite for its protection."To summarize Mill's summary the first maxim is this: if what I do is my own personal business, then it's none of your business. The second maxim is this: what I do with my liberty must not interfere with your liberty.
So how does Mill's theory of liberty play out in real life? It sounds simple when you read his maxims but becomes more complicated when you try to apply them to real-life situations. Let's look at one example: the law requiring people to wear protective helmets when riding motorcycles. Mill acknowledges that "it is a proper office of public authority to guard against accidents..." so you might assume that Mill would agree there needs to be a law that motorcyclists should wear protective helmets. This will help protect them from grave injury or death in case of an accident. But Mill also says
"Nevertheless, when there is not a certainty, but only a danger of mischief, no one but the person himself can judge of the sufficiency of the motive which may prompt him to incur the risk..."In this case the danger of mischief is the risk of having an accident while riding a motorcycle. The reader is led to assume that Mill believes the risk should be left entirely up to the individual riding the motorcycle. The government has no right to prevent him from riding the motorcycle simply because he may have an accident. If he believes he won't have an accident, then it's his personal decision. The government has no right to force him to wear a protective helmet.
Sometimes liberty remains a fuzzy concept under Mill's theory. Loitering is a fuzzy example. Mill says that "Idleness...cannot without tyranny be made a subject of legal punishment." Many places have loitering rules or laws. Would Mill approve of loitering if women felt threatened by gangs of men hanging out on street corners with no apparent purpose? It comes down to this: which is more important, my liberty to hang out on street corners or a woman's liberty to walk about downtown without feeling threatened? How does Mill's theory of liberty decide this issue?
In some areas of modern life, Mill's theory will be perfectly clear. Mill says that "offences against decency" may be prohibited because they fall within the category of offenses against others. Here he's in agreement with modern America law. I can legally watch X-rated movies in the privacy of my own home but I can't legally project them onto the side of a building in downtown Nashville. Society won't let me. But if we want to retain our civil liberties then there are certain things society is powerless to stop. "Fornication, for example, must be tolerated, and so must gambling..." says Mill because "...society has no business, as society, to decide anything to be wrong which concerns only the individual." Besides, as a practical matter we may as well tell the wind to stop blowing. Men have been fornicating and gambling for several thousand years now. They won't stop just because some folks think it's wrong to fornicate or gamble. Mill accepts these limits on liberty and thinks we should too.