Peter Singer, philosopher

When we talk of power we think of tangible institutions, governments, armies, big business. But how about the power of ideas? From Socrates to Marx philosophers have challenged us to rethink the way we see the world and our place in it. So too Australian philosopher Peter Singer. His writing on the relations between rich and poor, on medical ethics and animal rights have seen him variously described as the most influential and dangerous philosopher alive today. Does he believe ideas can change the world?