Article 4, Section 2, Clause 3
Document 1
William Blackstone, Commentaries 1:411--13
1765I. As to the several sorts of servants: I have formerly observed that pure and proper slavery does not, nay cannot, subsist in England; such I mean, whereby an absolute and unlimited power is given to the master over the life and fortune of the slave. And indeed it is repugnant to reason, and the principles of natural law, that such a state should subsist any where. The three origins of the right of slavery assigned by Justinian, are all of them built upon false foundations. As, first, slavery is held to arise "jure gentium," from a state of captivity in war; whence slaves are called mancipia, quasi manu capti. The conqueror, say the civilians, had a right to the life of his captive; and, having spared that, has a right to deal with him as he pleases. But it is an untrue position, when taken generally, that, by the law of nature or nations, a man may kill his enemy: he has only a right to kill him, in particular cases; in cases of absolute necessity, for self-defence; and it is plain this absolute necessity did not subsist, since the victor did not actually kill him, but made him prisoner. War is itself justifiable only on principles of self-preservation; and therefore it gives no other right over prisoners, but merely to disable them from doing harm to us, by confining their persons: much less can it give a right to kill, torture, abuse, plunder, or even to enslave, an enemy, when the war is over. Since therefore the right of making slaves by captivity, depends on a supposed right of slaughter, that foundation failing, the consequence drawn from it must fail likewise. But, secondly, it is said that slavery may begin "jure civili;" when one man sells himself to another. This, if only meant of contracts to serve or work for another, is very just: but when applied to strict slavery, in the sense of the laws of old Rome or modern Barbary, is also impossible. Every sale implies a price, a quid pro quo, an equivalent given to the seller in lieu of what he transfers to the buyer: but what equivalent can be given for life, and liberty, both of which (in absolute slavery) are held to be in the master's disposal? His property also, the very price he seems to receive, devolves ipso facto to his master, the instant he becomes his slave. In this case therefore the buyer gives nothing, and the seller receives nothing: of what validity then can a sale be, which destroys the very principles upon which all sales are founded? Lastly, we are told, that besides these two ways by which slaves "fiunt," or are acquired, they may also be hereditary: "servi nascuntur;" the children of acquired slaves are, jure naturae, by a negative kind of birthright, slaves also. But this being built on the two former rights must fall together with them. If neither captivity, nor the sale of oneself, can by the law of nature and reason, reduce the parent to slavery, much less can it reduce the offspring.
Upon these principles the law of England abhors, and will not endure the existence of, slavery within this nation: so that when an attempt was made to introduce it, by statute 1 Edw. VI. c. 3. which ordained, that all idle vagabonds should be made slaves, and fed upon bread, water, or small drink, and refuse meat; should wear a ring of iron round their necks, arms, or legs; and should be compelled by beating, chaining, or otherwise, to perform the work assigned them, were it never so vile; the spirit of the nation could not brook this condition, even in the most abandoned rogues; and therefore this statute was repealed in two years afterwards. And now it is laid down, that a slave or negro, the instant he lands in England, becomes a freeman; that is, the law will protect him in the enjoyment of his person, his liberty, and his property. Yet, with regard to any right which the master may have acquired, by contract or the like, to the perpetual service of John or Thomas, this will remain exactly in the same state as before: for this is no more than the same state of subjection for life, which every apprentice submits to for the space of seven years, or sometimes for a longer term. Hence too it follows, that the infamous and unchristian practice of withholding baptism from negro servants, lest they should thereby gain their liberty, is totally without foundation, as well as without excuse. The law of England acts upon general and extensive principles: it gives liberty, rightly understood, that is, protection, to a jew, a turk, or a heathen, as well as to those who profess the true religion of Christ; and it will not dissolve a civil contract, either express or implied, between master and servant, on account of the alteration of faith in either of the contracting parties: but the slave is entitled to the same liberty in England before, as after, baptism; and, whatever service the heathen negro owed to his English master, the same is he bound to render when a christian.
The Founders' Constitution
Volume 4, Article 4, Section 2, Clause 3, Document 1
http://press-pubs.uchicago.edu/founders/documents/a4_2_3s1.html
The University of Chicago Press
Blackstone, William. Commentaries on the Laws of England: A Facsimile of the First Edition of 1765--1769. Chicago: University of Chicago Press, 1979.