In the 21st century, humanity is reaching new heights of scientific understanding - and at the same time appears to be losing its mind. How can a species that sequenced the genome, produce so much fake news, conspiracy theories, and 'post-truth' rhetoric? Rationality guides the reader through the basics of logic and critical thinking and helps us to make rational choices alone and with others. Steven Pinker's follow-up to 'Enlightenment Now'.