The common sense observation that there are people who can’t direct their own lives well
That is not merely what Aristotle was claiming. In his Politics he stated: “
The rule of a master, although the slave by nature and the master by nature have in reality the same interests, is nevertheless exercised primarily with a view to the interest of the master.” He saw natural slaves as tools to be used for the benefit of their master, saying: “
a slave is a sort of living piece of property; and like any other servant is a tool”.
Ironically, his belief in natural slavery was itself based upon his teleology i.e. there are some people who are naturally inferior whose
purpose or end is to be enslaved “primarily with a view to the interest” of the inherently superior, as he noted: “
[T]he lower sort are by nature slaves, and it is better for them as for all inferiors that they should be under the rule of a master” with the inevitable corollary being that they have “
no deliberative faculty at all”.
He was of the belief that the slaves have no reasoning power. And he justified all of this based upon metaphysics, namely the “
ladder of nature” - which isn’t found in Sacred Scripture or Tradition.
How is this consistent with Christian moral doctrine or that man was created in the image of God?
It was the very idea condemned by Pope Paul III in 1537, when it was used by some errant Spanish philosophers against the Native Indians of the Americas:
The enemy of the human race, who opposes all good deeds in order to bring men to destruction, beholding and envying this, invented a means never before heard of, by which he might hinder the preaching of God’s word of Salvation to the people…to publish abroad that the Indians of the West and the South, and other people_ of whom We have recent knowledge should be treated as dumb brutes created for our service, pretending that they are incapable of receiving the Catholic Faith._
We, who, though unworthy, exercise on earth the power of our Lord and seek with all our might to bring those sheep of His flock who are outside into the fold committed to our charge, consider, however, that the Indians are truly men and that they are not only capable of understanding the Catholic Faith but, according to our information, they desire exceedingly to receive it.
Sepúlveda had been relying on the Aristotelian “
natural slavery” argument, which eventually led to the papal bull Sublimis Dei by Pope Paul III, which declared that indigenous people were rational beings and not “
dumb brutes created for our service”, incapable of exercising self-government, free will, and rational thinking, and therefore of receiving the message of Christ.
The Church has never accepted as a basis for slavery that some men are naturally inferior to others such that they lack reasoning power and, therefore, are naturally slaves. This was the premise of Aristotle’s argument in favor of the practice (Aristotle, Politics, 1254b16–21). It is clearly rejected by Paul III in
Sublimis Deus
