I think the most straightforward definition of slavery would be a system in which human beings can be bought and sold as individuals (in contrast to serfdom, in which humans come with the land) and in which the condition of being buyable and sellable has no expiration date (in contrast to indentured servitude, in which a person’s labor can be bought and sold but the person is not permanently classified as property). Defined in this way, slavery was certainly not outlawed during the Middle Ages, though by and large it did not flourish except on the frontiers of Christendom (due to the Church’s strictures on enslaving Christians and to the widespread practice of freeing slaves once they had been Christianized and assimilated).
Edwin
I do not purport to be a historian, but long ago I took a graduate course in legal history, and have read the old slave cases of my state, and some history of slavery in places other than the U.S. It is interesting that in those parts of the West where slavery had existed for centuries, it was relatively benign as slavery went, largely because the Church had rules relating to it that had been developed over time. Under most systems derived from Roman law, and over which the Church had a great deal of influence, slavery was considered a temporary condition (though, doubtless, it was abused), and as such it tended to be a “revolving door”. Because it was a “revolving door”, any slave was, at least theoretically, going to be a free person at some time. For that reason, they had rights, no doubt often breached, but often respected, because one could never be sure he would not someday face a former slave as a free man.
The English had no significant history of slavery prior to the 17th Century and, when casting about for a system to define and regulate it when slavery proliferated in English trade and in the colonies, they resorted to the Common Law regarding chattels. (“Chattel” is derived from the word “cattle”, but extends to all tangible personal property under the Common Law, even today) Thus, under “Chattel Slavery”, a system all its own, a slave had no rights at all; any more than a cart or a pitchfork or a horse had rights. No doubt some slaveowners living under the English Common Law were decent people and treated slaves reasonably well. Some freed their slaves. But the law certainly didn’t require that they do any of that, and indisputably, many did not. And since slave status, like chattel status generally, was immutable, there was the assumption that neither the slave nor his descendants would ever become free. Thus, for example, the Dred Scott decision was perfectly consistent with American Law, which was derived from English Common Law. A wagon wouldn’t become anything other than a wagon by crossing from Missouri to Illinois, and neither would a slave. I’m not justifying it, but that’s why it was decided the way it was.
When Louisiana became a state, chattel slavery ill-fitted the existing Continental model. It is interesting to note that there is a great deal of racial admixture in those former slave-holding nations that were under Roman-derived legal systems, (including southern Louisiana) whereas there is much less in those that were under English Common Law-derived systems, and it has been speculated that the differences in the laws of slavery are responsible for those differences in racial admixture.