Slavery is an institution by which sapient individuals are held as property by other persons and compelled to perform labour for them. Which is about as far as it is possible to define slavery, since the detail varies tremendously.
The most widely known form of slavery is probably that known as "chattle slavery" - wherein enslaved persons are bought and sold at market in much the same manner as animals. Other forms have existed historically, most notably elective slavery (where the slave enters into the condition as a form of bankruptcy) and judicial slavery (where slavery is imposed by a court of law as a punishment for crimes).
Variations occur in how a person may enter slavery (Can it be imposed by force1, and if so who may impose it? Can someone be born a slave? Can it be entered voluntarily? Is anyone exempt from enslavement?), who may own slaves (are they available on the open market or do all slaves belong to the King?) and whether they can be freely transferred (if you accept a bankrupt as your slave, can you sell him on?). Exiting slavery is just as variable.
In some cases being an ex-slave had its own restrictions, in others they returned to being part of the general population.
The condition of slaves down the ages also varied immensely - under some systems (or parts of systems) slaves were treated little better than animals, in others slaves could become wealthier than many free men (although most didn't). Whether a slave could own property, marry or bear arms were all highly variable. Some forms of slavery forbade a slave to learn to read or write - in others it was normal to have a slave as a clerk.
Legal codes would also vary as to what a slave could make contracts for (if anything), what he could be held responsible for and what punishments could be imposed - those for fleeing slavery or for any display of defiance towards an owner (or sometimes any free person) were usually harsh and exemplary and sentences in general would be more severe than for the free population. However, in some cases a master would be held liable for the offences of his slaves as well as or instead of them.
The "sapient individuals" note at the start is an important one - and this may be subject to legal and moral debate. Where slaveowners felt the need to make a moral justification of their position (and many cultures did not) denial of the slaves humanity (or at any rate equal capacity) was occasionally used. This becomes a lot more pertinent when the slaves are not the same species as their owners - Artificial Intelligences, bioroids and extensively genengineered humans might all face this, as might aliens or other fantasy races. Indeed any non-human sapient might conceivably be at risk of slavery2. More prosaically, nationality may be an important deciding factor.
Slavery should be distinguished from other forms of unfree labour, not least because of the normal lack of reciprocal obligation on the part of the owner - an indentured labourer, serf or apprentice is not free to change jobs or withdraw their labour, but their master does have contractual obligations towards them and they remain a person in law.
- LEV25, containing a substantial chunk of an ancient legal code that concerns slavery and release from slavery.
- An essay on slavery in Saxon England.
Game and Story Use
- Slavery was a normal part of many (if not most) pre-modern societies - that it's normally absent or illegal in most RPG worlds bespeaks the limited understanding of most writers. It's sensible to have some nations that don't practice slavery, but bizarre to have a world in which no-one does.
- In general, this is an excellent source of values dissonance - many players will think it quite normal for their character to regard slavery as an umitigated evil. In some settings this will not be a problem, but if their character were, for example, a Roman or Greek citizen, they will need to recognise that this is a very wierd point of view and liable to get them into trouble if they express it too loudly. The GM should probably ask the player to justify how his character came to such a deviant opinion and/or talk it through with them before it causes a problem in play.
- Certainly, players brought up on tales of antebellum America should not be encouraged to expect underground railroads bundling escaped slaves out of Imperial Rome (for example).