If the view given in the text be sound, it illustrates very strikingly the difference between natural instincts and moral intuitions. For the impulse to requite a service is, on its emotional side, quite different from that which prompts us to claim the fruits of our labour, or ``a fair day's wages for a fair day's work''. Still, our apprehension of the duty of Gratitude seems capable of being subsumed under the more general intuition `that desert ought to be requited'.