There is no duty more obligatory than the repayment of kindness.
There is no duty more indispensible than that of returning a kindness.
It is our duty, my young friends, to resist old age.
It was fear that was then making you a good citizen, which is never a lasting teacher of duty.
There is not a moment without some duty.
There is no moment without some duty.
The first duty of a man is the seeking after and the investigation of truth.