Though long estranged from legal reading and reasoning, and little familiar with the decisions of particular judges, I have considered that respecting the obligation of the common law in this country as a very plain one, and merely a question of document. If we are under that law, the document which made us so can surely be produced; and as far as this can be produced, so far we are subject to it, and farther we are not. Most of the States did, I believe, at an early period of their legislation, adopt the English law, common and statute, more or less in a body, as far as localities admitted of their application. In these States, then, the common law, so far as adopted, is the _lex-loci_. Then comes the law of Congress, declaring that what is law in any State, shall be the rule of decision in their courts, as to matters arising within that State, except when controlled by their own statutes. But this law of Congress has been considered as extending to civil cases only; and that no such provision has been made for criminal ones. A similar provision, then, for criminal offences, would, in like manner, be an adoption of more or less of the common law, as part of the _lex-loci_, where the offence is committed; and would cover the whole field of legislation for the general government. I have turned to the passage you refer to in Judge Cooper's Justinian, and should suppose the general expressions there used would admit of modifications conformable to this doctrine. It would alarm me indeed, in any case, to find myself entertaining an opinion different from that of a judgment so accurately organized as his. But I am quite persuaded that, whenever Judge Cooper shall be led to consider that question simply and nakedly, it is so much within his course of thinking, as liberal as logical, that, rejecting all blind and undefined obligation, he will hold to the positive and explicit precepts of the law alone. Accept these hasty sentiments on the subjects you propose, as hazarded in proof of my great esteem and respect. TO BARON HUMBOLDT. MONTICELLO, June 13, 1817.