'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. That the only purpose for which power can be rightfully exercised over any member of a civilized community, against his will, is to prevent harm to others. His own good, either physical or moral, is not sufficient warrant.'
What could be clearer? Except it isn't clear: it depends on what you mean by harm. Does hate speech harm minorities? Does sexist language harm women, by making them less credible in the eyes of society? Philosophical principles are like credit agreements: the headlines are convincing, but the small print catches you out.
There must be a reason why the big bang happened, but that does not mean it happened for any end or goal
The idea that everything is as it is for a reason is the assumption behind most of philosophy. If we thought that things just happened, we would not bother to try to work out their causes. But then nor would we assume that longer days meant more sunshine meant warmer weather. But this principle is crucially different from the one that says everything must have a purpose.
Good as a 'mean' that stands between two bads: that of excess and that of deficiency
Moral thinking is steeped in sharp dualities: Good v Evil, God v Satan, Right v Wrong, Heaven v Hell. Popular mythology, from humanity's fall from grace in the Garden of Eden to Star Wars, is full of tales of people going over to the dark side. But long before modern psychology told us that we all have our shadow side, an Ancient Greek philosopher came up with an idea that was even more subtle: it is not that there are shades of grey between moral black and white - good and bad aren't opposites at all. Rather, the good is a 'mean' that stands between two bads: that of excess and that of deficiency. Courage, for instance, is the mean between the excess of rashness and the deficit of cowardice. Mercy is the mean between the excess of vengefulness and the deficiency of surrender. It's a brilliant idea that utterly transforms how you look at right and wrong.
A theory is only scientific if you know what would disprove it
Common sense once held that a theory was scientific if you knew how to prove it. That's why conspiracy theories are nonsense: no matter what the evidence, believers insist this proves how tough the cover-up is. Similarly, you could argue that the theory that God does what is best for us is not scientific, because whatever happens, believers insist it must be for the greater good. God's goodness may be a theological claim but it's not evidential.
'Since reason commands that such actions should take place, it must be possible for them to take place'
How often do people insist that 'Something should be done' even though they've no idea what that something is? But unless you have an idea what should be done, how do you even know that it's possible to do anything at all? It makes no sense to say something should be unless it actually can be. In other words, if a prescription is truly rational, then it must be possible. Which means if it looks rational, but isn't possible, it isn't rational at all, like expecting a system to run on debt indefinitely.
'A weaker evidence can never destroy a stronger'
'A wise man proportions his belief to the evidence' sounds like advice you know already. But it's more easily agreed with than followed, and the results can be uncomfortable. Sounds obvious, but when it comes to the miraculous, has the testimony of any witness ever been stronger evidence than the testimony of all the rest of life, which tells us that nature's laws do not admit exceptions? If not then anyone who claims to base belief on evidence can never believe in miracles.
The difference principle states that increases in inequality are only permissible if they benefit the worst-off members of society
If some philosophical principles seem so obvious as not to be worth stating, others shatter consensus. Such is the case with Rawls's difference principle, which the Liberal Democrats once considered adopting as policy. This states that increases in inequality are only permissible if they benefit the worst-off members of society. It sounds radical, but after recent events with bankers' bonuses, fewer people now believe that concern about growing pay at the top of the economic scale is pure envy. The difference principle states that it is fine for the rich to get richer only if the poor always become richer than they would have done had the wealthy been held back. It's a liberal compromise between the socialist demand for equality and the neo-liberal disregard for equality.
If a man is sending a woman mixed messages, the simple answer is, he's just not that into her
In an age of five-blade razors, the one wielded by William of Occam is ironically named, for it is the requirement not to multiply entities beyond necessity. So, if you can explain the workings of the world by postulating only the existence of matter, you should not prefer an explanation that also posits ectoplasm, unless that more complicated theory can explain more. The principle is also known as one of economy of explanation: all other things being equal, a simpler explanation is more likely to be true than a complicated one. It's a principle that has even found its way into Sex And The City: if a man is sending a woman mixed messages, the simple answer is he's just not that into her.
The morality of war is determined both by the reasons for starting it and its conduct once begun
Thinkers have long pondered when war is morally justified, but modern theories of just war are little more than amendments to those set down by Thomas Aquinas in the 13th century. The morality of a war is determined both by the reasons for starting it and its conduct once begun. To wage war, the cause needs to be just, it must be waged by an army with legitimate authority, it must be fought for the right intentions, there must be a good probability of success, the response must be proportionate, and it must be the last resort. Armies must use proportionate force and discriminate between combatants and innocent civilians.
Cited from: http://www.dailymail.co.uk/home/moslive/article-1279320/Ten-greatest-Philosophical-principles.html#ixzz4KDSuHQpx