In the age of social media, it has become easier than ever to spread misinformation and falsehoods.
This has been a problem particularly with people's attitudes to scientific issues such as climate change and vaccination.
Physicist, cancer researcher and science journalist David Robert Grimes has written a new book, The Irrational Ape, in which he argues that critical thinking can save the world.
David points out that we are entitled to our own opinions, but not to our own facts, and that when it comes to evidence "it has to be what is objective and what is measurable."
He joined us on The Last Word to discuss the concept further, and why flawed logic puts us all at risk.
Listen to the interview in full by pressing the play button on this page.