Antoine basically believes in two things: stuff that exists and stuff that doesn't exist. No, not like "adorable kittens" (does exist) vs. "a delicious bowl of pea soup" (does not exist).
For him, the stuff that exists is what's physically real, like the objects he can see and touch. Other stuff like thought and personality aren't real, but are just abstract things invented by the human brain. Because of this, Antoine thinks that one of the most important things he can know about people is their appearance, since this is the part of them that actually qualifies as "real."