Did slave owners fully believe that slaves were not human or was that just their excuse to own them?

by Magnaleo

This question is regarding American slavery. Slaves were regarded as property, so not humans the same way free persons and white people were. Was this done just as a legal justification (and perhaps also for one's own conscience) for the owning of slaves, or did people wholeheartedly believe that slaves were nonhuman?

throwawayonmybody

Here is a previous answer from u/NumisAl to a similar question.