How to use "rational" in a sentence

Sentences

He had no rational reason to entertain such dark thoughts

As far as she could see, only one rational explanation presented itself

At the same time, she knew this wasn't a rational thought; the explanation, whatever it might be, was not that simple

"And if I don't stay here, if I walk away and get a job at a civilian research center, that'll be just one less rational voice in this place