In a given situation, it is rational to accept as true what the best available evidence and the most careful thinking indicate to be true.

Rational

In accordance with the rules of effective thought concerning coherence, consistency, practicability, simplicity, comprehensiveness, looking at the evidence and weighing it carefully, not jumping to conclusions, and so on. Rationality may not guarantee truth; all the evidence and everything we believe may point to one conclusion, and yet later generations, who know things that we do not, may see that our conclusion was incorrect. It was rational thousands of years ago to believe that the earth was flat, even though it was not true. It is not rational for us to believe the same thing, for our evidence and all sorts of other beliefs indicate, rather, that it is rational to believe that the earth is (more or less) spherical.

Best Available Evidence

The most reliable and pertinent information and data available at the time to support a decision or conclusion.

Careful Thinking

The process of thinking in a judicious, meticulous manner, ensuring attention to detail and consideration of all aspects before forming a judgment or conclusion.