For if every instrument could accomplish its own work, obeying or anticipating the will of others, like the statues of Daedalus, or the tripods of Hephaestus, which, says the poet, "of their own accord entered the assembly of the Gods;" if, in like manner, the shuttle would weave and the plectrum touch the lyre without a hand to guide them, chief workmen would not want servants, nor masters slaves.
Aristotle. Politics 1-4

These days, slavery is regarded as barbaric and cruel. For one free man to enslave another is to take away his freedom, and is tantamount almost to murdering him. In this view, the ancient slaveowners of Greece and Rome were morally deficient. If the institution of slavery is now almost entirely absent from Western society, it is regularly held to be the consequence of moral progress: we are, quite simply, better people than ancient Greek and Romans.

But, seen from Idle Theory, slavery was never a matter of one free man depriving another free man of his liberty. It was never as if one free and leisured man pursued and captured another free and leisured man, and forced him to become his slave. Instead it was that unfree and busy men captured and enslaved other unfree and busy men, in order to free themselves from toil, and lead lives of leisure. And, furthermore, they did this because it was the only way that they could attain a life of leisure - a life in which they could become poets and historians, mathematicians and philosophers.

In a circumstance where men have to toil for 90% of their time to earn a meagre living, if anyone wants complete freedom, they can only achieve it by making other people work for them, and thereby free them from their work. The alternative was to continue working day in, day out.

For a man living a 10% idle life, the prospect of becoming a slaveowner offered the prospect of 100% idleness - an order of magnitude improvement on his previous condition, and a powerful incentive.

Enslavement, it may be supposed, simply involves one individual capturing another, chaining or hobbling him, and obliging him on pain of death to work for him. However, once enslaved, the slave must still work to support himself, and so only his idle time is available for work as a slave. And therefore in a 10% idle society, any individual who desires a 100% idle life must have at least 9 slaves, each of whom performs 10% of his work for him. If he owns more, then cannot supply him with any more leisure, but can only work to supply him with luxuries and amusements.

For any individual to enslave another, he must first have the idle time in which to make ropes or chains, and secondly the idle time in which to pursue and capture slaves, and thirdly the time in which to impose his will on an unwilling new slave, with threats and blows. And therefore it follows that there is some minimum of social idleness below which it is impossible for anyone to enslave anyone else, not only because there is not the time available to go through the process of enslaving another person, but anyway because such slaves would have little idle time to put at the disposal of their master. In a society at or near zero idleness, there can be no slavery. It is only above some threshold of social idleness that slavery becomes a workable proposition.

Now in the process of capturing slaves, it must be supposed that prospective slaves will attempt to flee, and need to be pursued before they are captured. However, a 10% idle man is someone who must spend 90% of his time working, and he cannot work and flee at the same time. It is only in their idle time that anyone can flee. And so a 10% idle man can only spend 10% of his time fleeing from a pursuing slavemaker. And equally, a 10% idle slavemaker can only spend 10% of his time pursuing a fleeing prospective slave. And so where prospective slaveowner and prospective slave are equally idle, there is at best an even chance of one successfully managing to enslave the other - it being perfectly possible that the roles may be reversed, and the prospective slave enslaves the prospective slaveowner.

But once a slaveowner has one slave, and his idleness has been raised to 20%, then he is able to spend more time pursuing 10% idle prospective slaves than they can spend trying to escape. And so as he acquires two, three, or four slaves, capturing new slaves becomes progressively easier. And once he has nine slaves, he achieves perfect idleness. Except, of course, that he will need to keep his slaves in order, and give them instructions. But then this management problem may be solved by acquiring more slaves, and appointing an experienced slave as their manager, and rewarding this manager with a little idle time of his own.

In this example, a potential slaveowner has a strong incentive - the prospect of complete freedom - to acquire slaves. But the slaves, by contrast, have no great incentive to escape, for if they do escape their idleness only increases from 0% to 10%. And a slaveowner may reduce this incentive by promising medical assistance and an assured food supply and the prospect of promotion in the ranks of slaves.

In the case of 10% social idleness, a prospective slaveowner has a strong incentive to acquire slaves, and his slaves have little incentive to escape. However, in a circumstance of 50% social idleness, there is less of an incentive to a prospective slaveowner, because he is already 50% idle, and moving from 50% idleness to 100% idleness is less compelling than that of exchanging 10% idleness for 100% idleness. And equally, since men are generally more idle, 50% idle prospective slaves can flee slavery for longer than 10% idle prospective slaves, and so acquiring slaves is more difficult. And when these slaves have been acquired they have a much stronger incentive to escape, because by escaping they exchange a life of zero idleness for one of 50% idleness, rather than a mere 10% idleness. However, at 50% idleness, a slaveowner only requires one slave to live a life of perfect idleness.

As social idleness rises rises, due to technological innovation, individual slaveowners need fewer and slaves, and more and more people own slaves. Society moves from few slaveowners each supported by many hard-working slaves, to many slaveowners each supported by a few largely idle slaves. Extreme social inequality is replaced by a general equality.

Furthermore, as social idleness rises, the incentive to own slaves decreases, and the difficulty in capturing and keeping slaves increases. At or approaching 100% idleness, the incentive to acquire slaves falls to zero, and the difficulty in capturing and keeping them becomes very high. In such circumstances, it is simpler and easier for a potential slaveowner to abandon any idea of enslaving anyone, and simply do the work himself, what little of it needs to be done. Thus at some degree of social idleness, a crossover point is reached where the benefits of slave-owning are outweighed by its costs.

And therefore it is concluded that the institution of slavery is likely to primarily found in low idleness societies. Slavery is progressively abandoned as social idleness rises, not because people's moral standards rise, but because slavery simply ceases to be a profitable enterprise.

And if the ancients were to be given the opportunity to answer their high-minded modern critics, they might point out that these critics are beneficiaries of technologies which never existed in ancient Greece or Rome: "Your shuttles weave and your plectrums touch the lyres without hands to guide them, and therefore you have no need for slaves. Do not judge us hastily, who wove long hours at the shuttle, if we had need of slaves. You have yourselves benefitted from the achievements of Greece and Rome, and therefore you also have benefitted from their slaves. And there may come a day when you too will work the shuttle again, and face again the same stark choices that we once faced."

The Enslavement and Consumption of Plants and Animals

One modern parallel to slavery may be found in human treatment of plants and animals. Humans not only enslave animals in order to carry burdens, haul carts and ploughs, but they also kill and eat both plants and animals, and burn and dismember plants.

But, in this respect, humans faced two stark options: either they enslaved and killed and ate animals and plants, or they died of starvation. To opt to die of starvation was unthinkable - and so humans enslaved and ate plants and animals.

And human attitudes to plants and animals parallels the attitudes of slaveowners in antiquity to their slaves: that they are a lower form of life, devoid of feelings, fit only to be enslaved and consumed.

However, in recent times, technological innovation in the form of tractors and cars has acted to emancipate many animals from work. Tractors rather than oxen pull ploughs. Cars rather than horses carry people. Burglar alarms replace guard dogs. Mousetraps replace cats. And the emancipated horses and dogs and cats are retained as pets and companions, and very often treated as members of human families.

The same has yet to happen with human food sources. Modern humans still need to kill and eat plants and animals in order to survive. But if it became possible for humans to cheaply produce proteins and carbohydrates synthetically, from carbon and hydrogen and oxygen and nitrogen, then it would no longer be necessary to grow fields of wheat and barley, or have cattle and sheep farms. Every form of farming would cease. Herds of cattle and sheep would vanish, along with fields of corn and wheat. And the highly selected domestic varieties of animals and plants would, left to their own devices, revert gradually to their original wild types. A landscape of farms would revert to wilderness and forest.

And at the same time, this emancipated natural world would be revalued. Much as modern cats and dogs are accorded equal rights as humans, so every kind of plant and animal would be accorded equal status as human life. It would become a crime to chop down a tree, to prune a rose bush, or to mow a lawn.