Some questions have troubled us for generations. If you have promised to lend your favourite sword to a colleague, but they have since gone dangerously mad, are you morally bound to keep your promise? If a murderer comes to your house looking for your best friend, is it immoral to lie to them about where she is?

Now, one man has written a book claiming to have all the answers. Not a philosopher, not a scientist, but a comedy writer. Michael Schur hardly seems the model for a modern PlatoOne of the most important Ancient Greek philosophers. : his previous credits include sitcoms The Office, Brooklyn Nine-Nine and Parks and Recreation.

Yet, he has done a great deal to popularise moral philosophy through his hit TV series The Good Place, which considered the ideas of history's greatest thinkers about how to lead a good life.

And in his latest book, How to Be Perfect, he is trying to go further still in teaching us all how to use philosophy to be better people.

The problem he faces is that philosophers themselves do not agree on how to be good. There are three major schools in Western moral philosophy: consequentialism, deontologyAn ethical theory invented by German philosopher Immanuel Kant. Its name comes from the Greek word deon, meaning duty, because it stresses the importance of clear, universal rules in guiding our actions. and virtue ethicsA school of ethics that can be traced back to Plato's successor, Aristotle. Its most prominent modern advocates have been women: English philosopher Philippa Foot, Irish thinker Iris Murdoch and American academic Martha Nussbaum.. And all have different answers.

Consequentialists believe the outcomes of our actions define whether or not they are morally good. The most influential kind of consequentialism is utilitarianismA theory of morality invented by English thinker Jeremy Bentham, who also devised a special kind of prison known as a panopticon., which argues that we must try to maximise pleasure and minimise pain.

Take the classic trolley problem. A runaway trolley is hurtling down a set of tracks on which five unwitting pedestrians are standing. By pulling a lever next to you, you can divert it onto a different set of tracks with just one hapless bystander. For a utilitarian, the answer is clear: one death is less than five deaths. Pull the lever.

Deontologists believe to live morally, we must obey certain universal rules. The most essential rule is always to treat others as ends, rather than as meansThe principle that Immanuel Kant placed at the very heart of his ethical theory. It means we must always respect the goals of others, and not simply use them to achieve our own goals.. For them, pulling the lever is not an option: it means treating one victim as a means of saving the other five.

Finally, virtue ethicists think the solution must be found long before you even get to the lever. They believe we should seek to cultivate the right kind of personality: kind, generous, courageous. Then, when we find ourselves in the middle of a set-piece ethical dilemma, we will know what to do.

But virtue ethicists are not so clear on what a virtuous person actually looks like. AristotleA student of Plato, tutor to Alexander the Great and the father of political philosophy. suggested that we should moderate everything. That means being fairly kind, fairly generous, fairly courageous - but not too much of any of them.

Some philosophers simply ignore all three. For Jean-Paul SartreA French philosopher who is perhaps the most famous name associated with existentialism. He was married to Simone de Beauvoir. there was no rule or authority that can make our decisions for us. We as individuals must accept full responsibility for our own choices.

Ancient Chinese philosophy proposed a different approach: role ethics. Confucius argued that we lead a morally good life by carrying out our role in the community. The ethical person is dutiful to their parents and children, and in accord with their emotions.

Yes: We are the heirs to thousands of years of thinking about difficult ethical questions. We should use these tested, timeless ideas to make the right decisions in our own lives.

No: Every moral philosophy is a product of its own era and the prejudices of that era. We now live in a scientific age, and we should rely on science to lead good lives, not outdated ethical ideas.

Or... We simply cannot think about morality without thinking philosophically, but the world is too complex to be boiled down to any one school of thought. We should adopt a flexible moral philosophy.