Full Idea
A rational animal is one that is a normative-reflective possessor of the concepts of necessity, certainty and unconditional obligation.
Gist of Idea
Rational animals have a normative concept of necessity
Source
Robert Hanna (Rationality and Logic [2006], 4.0)
Book Reference
Hanna,Robert: 'Rationality and Logic' [MIT 2006], p.77
A Reaction
The addition of obligation shows the Kantian roots of this. It isn't enough just to possess a few concepts. You wouldn't count as rational if you didn't desire truth, as well as understanding it. Robots be warned.