Collocations for rational - adj.

be, seem
It all seemed quite rational to me.

highly, very
completely, eminently (formal), entirely, fully, perfectly, quite
At the time she was perfectly rational.

purely, strictly
essentially
Humans are essentially rational beings.

apparently
economically
With children working from the age of ten, large families were economically rational.

about
Try to be rational about it.

Rational is used with these nouns:
agent, approach, argument, basis, being, belief, calculation, choice, debate, decision, deliberation, discussion, enquiry, expectation, explanation, faculty, justification, manner, mind, number, person, reason, response, self-interest, soul, thinking, thought, understanding