XV.8 Needlessness of slavery here
We must then limit natural slavery to certain specific countries of the earth. In all the others it seems to me that however hard the labors society demands, they can all be done with free men.
What makes me think so is that before Christianity had abolished civil servitude in Europe, work in the mines was regarded as so hard that people thought it could be done only by slaves or criminals. But today we know that the men who are employed there live well.  Small privileges have encouraged this profession ; an increase in work has been tied to an increase in earnings, and they have been brought to like their situation better than any other they might have adopted.
No labor is so hard that it cannot be scaled to the strength of the man who performs it, provided it be reason and not avarice that determines it. It is possible, thanks to the convenience of machines invented of applied by art, to accomplish the forced labor that elsewhere is imposed on slaves. The Turkish mines in the Banat of Timişoara were richer than those of Hungary, and they did not produce as much, because the Turks never imagined anything but the labor of their slaves.
I do not know whether it is the mind or the heart that dictates what I am saying here. There is perhaps no climate on earth where free men could not be induced to work. Because the laws were bad, men were thought to be slothful ; because those men were slothful, they were made slaves.