Final answer:
Montesquieu critiqued slavery but also suggested situations where it could be tolerable. Enlightenment thinkers like Thomas Jefferson experienced a conflict between the ideals of liberty and the reality of African slavery, often justifying it with social contract theory and racist pseudoscience despite contradictions to Enlightenment principles.
Step-by-step explanation:
Montesquieu, a French philosopher, had complex views on slavery. While he critiqued it in his work 'The Spirit of the Laws,' arguing it went against natural human liberty, he nuanced this by suggesting that in some climates and situations, it could be more tolerable. Like Montesquieu, other Enlightenment thinkers in Europe and America, such as Thomas Jefferson, experienced a dissonance between their ideals of liberty and equality and the reality of African slavery.
Jefferson, in particular, while acknowledging the inalienable rights of all men, owned slaves himself. He foresaw difficulty in the abolition of slavery due to potential race wars and posited the inferior intellectual capacities of Africans, a belief rooted in the racist pseudoscience of his time. Despite these contradictions, the Enlightenment ideals influenced gradual emancipation in the North post the American Revolution, although the South held on to slavery based on race.
In conclusion, the justifications for slavery during the Enlightenment were often based on social contract theories, scientific racism, and concerns over political instability, highlighting the profound contradictions between the era's ideals and its societal structures.