On a former occasion I took the liberty of consulting you on an interesting and important subject of Natural Science, and feel myself much honoured by the attention you were pleased to show my letter, in giving it a reply so ample, so instructing, & so satisfactory. I only regret that I did not apply for permission to publish it.

I am fully convinced of the correctness of the observation contained in your letter respecting the Unity of the operations of Nature, & of the advantage to be derived to our memories by an artificial classification of her productions.

I am myself emphatically an Unitarian. I believe in the Unity of the Deity with my friends Cooper Priestley and other theologians, in opposition to the polytheism of the Athanasian creed. I believe in the Unity of Disease, in opposition to the nosological systems of Sauvages1 Sydenham Linnæus Cullen & other pathologists, with my truely worthy friend & preceptor in medicine the immortal Rush, for whom I shall ever feel a lively sense of gratitude for the innumerable instances of kindness & attention with which he honoured me, both during my pupilage, & after I graduated & practiced in that metropolis. But I must not permit my love for my departed master to carry me from my subject. And further, I believe with you and the learned M. Buffon the great advocate of individualism, in the Unity of the operations of Nature. Yet I cannot join M. Buffon in condemning all classification as injudicious.

Certainly the division of natural productions into Classes orders genera Species tribes sects & societies tho’ strictly artificial, facilitates the acquisition of a knowledge of the science of Nature. But among all the authors who have classified the productions of nature, I do not know that any one is intrinsically much better than another. Thus the classifications of Ray Klein Brisson Linnæus Cuvier Blumenbach2 Jussieu Hauy &c. have each of them their respective merits. But for the reason contained in your letter, I think that the systema Naturæ must ever remain the grand Book of Record among naturalists. This is the opinion of my worthy & learned friend Dr Saml L. Mitchill of N. York.

Our late departed friend Dr Benj. Smith Barton, whose death must long be deplored by every naturalist, to whom I took the liberty of showing your letter, requested me to state to you, that the observations of the Chevalr d’Abboville respecting the mammæ of the opposum being only discoverable during pregnancy or suckling her young is incorrect. He said he had fully proved that they were discoverable at all times.

I was not before aware that it had been ascertained that the ornithorynchus of New Holland was viviparous. But notwithstanding this fact, has it not in the aggregate as many characteristics of the Aves, as of the Mammalia & does it not want some of the most essential of the latter.

I should do an injustice to my feelings, on the present occasion, were I not to acknowledge that I have derived more instruction from reading your letter than from all the books which I have seen upon the subject of which it treats.

I formerly devoted much time & attention to the study of the natural sciences, but the pursuit of two professions, and the attention which I must necessarily bestow to the instruction of my pupils of both law & medicine, leave me little time to cultivate my former more favorite studies.

On the present occasion I wish your instruction on an important subject of national jurisprudence. I should be much gratified to know your opinion of the right of expatriation. The authorities on both sides of the question are so numerous & respectable as to render it difficult to decide. From my own view of the subject I should conclude that the ne exuere ligeantiam was not founded in law, & certainly not in reason

It cannot be founded in the law of Nature. For in a state of Nature, all ethical writers agree that every person has a right to emigrate to whatever place his convenience or his inclinations may lead him, & to occupy what ever lands he pleases: as all men are equal he owes allegiance to none.

It is not founded in the revealed Law. Numerous instances of expatriation are mentioned in both the old and New Testaments.

It is not founded in the law of Nations For altho’ Sir Edward Coke, Sir Mathew Hale, Sir William Blackstone, and other English jurists contend that it is the law of Nations, yet, in my humble opinion, the better authoriti[es] deny this position. Puffendorf Cicero3 Grotius Burlamaqui Locke Vattel &c. all admit the right of expatriation.

If it exist then in the United states it must be sought for in the Municipal Law. No such law, however, is expressed in either the constitution of the United states or their legislative acts.

It has been contended that we have adopted it by implication with the common law, & that it is founded in our lex non Scripta or unwritten Codes. But I should like to be informed how & at what time the United States in their federal & national capacity adopted a common law. If we have a common law, is it that of England? If that of England, whether intire or in part? & what part?

In the course of my researches in the science of Jurisprudence I have found so much difference of opinion of authors, so much contrariety of decision of courts, & so much difficulty on the subject, that I have determined to appeal to you for satisfactory information. Thus while Judge Chase, Judge Tucker, & Mr Madison, are of opinion that the common law of England has no binding authority in our national government, Judge Ellsworth Judge Washington & Judge Peters contend that the federal courts are invested with common law jurisdiction. Of the latter opinion is my father-in-law Judge Cooper, under whose direction my legal studies were conducted, & to whom I am indebted for whatever talents, as a lawyer, I may be thought to possess, as expressed in his edition of Justinian (p 405). altho he seems to have expressed a different opinion in Cooper’s Bankrupt Law (p 230 & 283).—

I must confess, that independent of any authorities upon the subject, considering the constitution as the warrant of attorney to the agents of the general government by their principals the several individual & independent states, which must be construed strictly, I cannot see how they are invested with any common law authority legislative executive or judiciary not expressly delegated to them

The federal government therefore, deriving all their powers from the states could not have adopted a Common law in their federal capacity.

But it has been said, that the states had granted it to the federal government by implication[.] The strict construction, however, which the constitution must receive would forbid such a conclusion. Add to this the twelfth article of the amendments to the constitution of the United States which expressly declares that “the powers not delegated to the United States by the constitution nor prohibited by it to the states, are reserved to the states respectively or to the people” Which according to Vattel & all writers on national law is a mere recognition of the law of nations.

The common law of England therefore, can have no more binding authority in our federal government than the Institutes of Justinian, or the Code Napoleon. It may be referred to as a known law but it is lex sub graviori lege, & has no binding authority. Otherwise we might boast our written constitution in vain.

It is admitted that the individual states may prohibit the emigration of their subjects. And admitting that every state in the Union had made such prohibition, which however is not the fact, yet it would not become the law of the United States unless expressly made so by constitutional or legislative regulation.

I am aware I stand in need of an apology for the liberty I have taken, but the interest I feel in the subject, the polite attention you were pleased to show my former letter, & your preeminent abilitie[s] to instruct, must plead my excuse.