This article investigates what constitutes good reason, in particular in scientific communication. I will start out with a general description of what scientists do and will identify the good argument as an integral part of all science. Employing some simple examples, I will then move on to derive some necessary conditions for the goodness of an argument. Along the way, I will introduce various basic concepts in logic and briefly talk about the nature of human knowledge. I will conclude by relating my discussion of good reasoning in science to critical thinking in general and explain why I believe that critical thinking is at the heart of a well-functioning liberal democracy.