In a perfect world, debates about the environment, public health and technology would be objective, reasoned, intellectually honest and grounded in evidence, but there are many forces working against that ideal. The first article in this section explains why in today's “post-truth” world such high expectations no longer hold and lies spread with abandon. People will always dispute the validity of facts, of course, but another story highlights research that shows they often go a step further and reframe an issue in untestable ways. That's a problem because while scientific truths are always provisional at some level, there are plenty of things we know with certainty. Our experts list more than a dozen irrefutable facts. At the end of the day, however, many people say that they trust scientists in general but part company with them on specific issues. Is it any wonder, given the circumstances, that current debates about public policy and personal choices are so fraught? We only hope that by learning more about our biases and tendencies, both innate and acquired, we may one day better grapple with the truth.