“My definition of a racist idea is a simple one: it is any concept that regards one racial group as inferior or superior to another racial group in any way. I define anti-Black racist ideas—the subject of this book—as any idea suggesting that Black people, or any group of Black people, are inferior in any way to another racial group.” 

Kendi clearly defines “racist idea,” as he will use the term often, in his Prologue. The language of a “group” is important to the rest of his text, for he works throughout to separate depictions of or ideas about black individuals from perceptions of black people as a category.

“Ibn Khaldun did not intend merely to demean African people as inferior. He intended to belittle all the different-looking African and Slavic peoples whom the Muslims were trading as slaves. Even so, he reinforced the conceptual foundation for racist ideas. On the eve of the fifteenth century, Khaldun helped bolster the foundation for assimilationist ideas, for racist notions of the environment producing African inferiority. All an enslaver had to do was to stop justifying Slavic slavery and inferiority using climate theory, and focus the theory on African people, for the racist attitude toward dark-skinned people to be complete.” 

Kendi explains that Ibn Khaldun and other thinkers centuries before America’s existence wrote about and worked to justify slavery through an environmental theory of racial difference. Without race, people from farther-distant countries were inherently less developed; enslavement was not yet connected to race, but location defined a person’s merit.

“Assimilationists argued monogenesis: that all humans were one species descended from a single human creation in Europe’s Garden of Eden. Segregationists argued polygenesis: that there were multiple origins of multiple human species.” 

As the ideas develop in the 17th century, Kendi defines the two schools of thought about human origins that came to define scientific debate about race. Separate political groups took hold of polygenesis and monogenesis, regardless of the religious implications of abandoning monogenesis. Because of the implications, this debate would continue for hundreds of years.