Natural Law

From Cicero:

True law is right reason in agreement with nature; it is of universal application, unchanging and everlasting.... It is a sin to try to alter this law, nor is it allowable to attempt to repeal any part of it, and it is impossible to abolish it entirely. We cannot be freed from its obligations by senate or people, and we need not look outside ourselves for an expounder or interpreter of it.... And there will not be different laws at Rome and at Athens, or different laws now and in the future, but one eternal and unchangeable law will be valid for all nations and at all times, and there will be one master and ruler, that is, God, over us all, for he is the author of his law, its promulgator, and its enforcing judge. Whoever is disobedient is fleeing from himself and denying his human nature....

...and later,

...our founding fathers believed in what the Declaration of Independence called “the Laws of Nature and of Nature’s God.” Our founders appealed to universal principles and natural rights that colonial Americans believed were being violated by British rule. They understood that there are objective principles of right and wrong, justice and injustice governing even the highest human authorities. As Martin Luther King, Jr. would later note, they understood that human law stands under the judgment of natural law and that human laws that fail to meet the standards of natural justice lack the power of just laws to bind in conscience.

Quoted in defense of marriage as opposed to same-sex "marriage", but applying to a lot of other questions.