“The opposite of nature is impossible.”

Grundrisse (1857-1858)
Source: Notebook V, The Chapter on Capital, p. 448.

Source: The Blind Watchmaker (1986), Chapter 2 “Good Design” (p. 41)

1850s, Speech at Peoria, Illinois (1854)
Context: Slavery is founded in the selfishness of man's nature — opposition to it, in his love of justice. These principles are an eternal antagonism; and when brought into collision so fiercely, as slavery extension brings them, shocks, and throes, and convulsions must ceaselessly follow. Repeal the Missouri Compromise — repeal all compromises — repeal the Declaration of Independence — repeal all past history, you still can not repeal human nature. It still will be the abundance of man's heart, that slavery extension is wrong; and out of the abundance of his heart, his mouth will continue to speak.

Summa Contra Gentiles, III,126,3

i. 17, f. 18^r
Commentarius in Posteriorum Analyticorum Libros (c. 1217-1220)

Source: The Art of the Commonplace: The Agrarian Essays

Source: Political Treatise (1677), Ch. 2, Of Natural Right
Context: In the state of nature, wrong-doing is impossible; or, if anyone does wrong, it is to himself, not to another. For no one by the law of nature is bound to please another, unless he chooses, nor to hold anything to be good or evil, but what he himself, according to his own temperament, pronounces to be so; and, to speak generally, nothing is forbidden by the law of nature, except what is beyond everyone's power.<!-- 23

On the Correct Handling of Contradictions Among the People
Original: (zh-CN) 马克思主义的哲学认为，对立统一规律是宇宙的根本规律。这个规律，不论在自然界、人类社会和人们的思想中，都是普遍存在的。矛盾着的对立面又统一，又斗争，由此推动事物的运动和变化。矛盾是普遍存在的，不过按事物的性质不同，矛盾的性质也就不同。对于任何一个具体的事物说来，对立的统一是有条件的、暂时的、过渡的，因而是相对的，对立的斗争则是绝对的。

XVII. That the World is by nature Eternal.
On the Gods and the Cosmos