I distinguish between the natural and accidental duty due to parents.

He took charge of things then as a natural duty but also, it seemed, with an effort.

The affection they felt for each other went beyond the natural duty of their blood tie.

You are far less numerous than your fellows over there, who are unwilling to perform any of their natural social duties.

They took it as their natural duty to protect this animal, both for its own sake and for that of the future world.

Manfred's natural Afrikaner duty of hospitality left him no choice.

In science, there is a natural duty to make what is known searchable.

He put his faith in the free individual, whose natural duty is to a higher truth than government bureaucracy.

And so the crew acknowledged him; to them he was a born Captain whom to obey would be a natural duty.

But she was satisfied to be able to fulfill her natural duty.