Thus in his defence of the Amistad captives he began with defining justice in the language of Justinian, "Constans et perpetua voluntas jus SUUM cuique tribuendi." He quoted on the same occasion from the Declaration of Independence, not by way of rhetorical embellishment, and not even as a valid human ordinance, but as a truth of nature, of universal application, the memorable words, "We hold these truths to be self-evident, that all men are created equal, and that they are endowed by their Creator with certain inalienable rights, and that among these rights are life, liberty, and the pursuit of happiness." In his vindication of the right of debate, he declared that the principle that religious opinions were altogether beyond the sphere of legislative control, was but one modification of a more extensive axiom, which included the unbounded freedom of the press, and of speech, and of the communication of thought in all its forms.

He rested the inviolability of the right of petition, not on constitutions, or charters, which might be glossed, abrogated or expunged, but in the inherent right of every animate creature to pray to its superior.
The model by which he formed his character was Cicero.

Not the living Cicero, sometimes inconsistent; often irresolute; too often seeming to act a studied part; and always covetous of applause.

But Cicero, as he aimed to be, and as he appears revealed in those immortal emanations of his genius which have been the delight and guide of intellect and virtue in every succeeding age.

Like the Roman, Adams was an orator, but he did not fall into the error of the Roman, in practically valuing eloquence more than the beneficence to which it should be devoted.