To live according to Nature is to act always with due regard to the fitness arising from the relations and qualities of causes and effects
 Samuel Johnson, The History of Rasselas, Prince of Abissinia (1759). copy citation

Context

“Let me only know what it is to live according to Nature.” “When I find young men so humble and so docile,” said the philosopher, “I can deny them no information which my studies have enabled me to afford. To live according to Nature is to act always with due regard to the fitness arising from the relations and qualities of causes and effects; to concur with the great and unchangeable scheme of universal felicity; to co-operate with the general disposition and tendency of the present system of things.” p. 92The Prince soon found that this was one of the sages whom he should understand less as he heard him longer.” source