The Third Guideline

https://www.lesswrong.com/posts/XPv4sYrKnPzeJASuk/basics-of-rationalist-discourse-1

Introduction

This post is meant to be a linkable resource. Its core is a short list of guidelines (you can link directly to the list) that are intended to be fairly straightforward and uncontroversial, for the purpose of nurturing and strengthening a culture of clear thinking, clear communication, and collaborative truth-seeking.

"Alas," said Dumbledore, "we all know that what should be, and what is, are two different things.  Thank you for keeping this in mind."

There is also (for those who want to read more than the simple list) substantial expansion/clarification of each specific guideline, along with justification for the overall philosophy behind the set.