Final answer:
Aristotle taught that human nature is divided between animal instinct and divine reasoning, emphasizing the unique human capacity for rational thought and virtue.
Step-by-step explanation:
The philosopher who taught that human nature is divided between animal instinct and divine reasoning is Aristotle. Aristotle's philosophy contends that while humans have instincts similar to animals, they are unique in their capacity for rational thought, which he defines as the unique function of human beings. This rational capacity is what allows for the development of virtue and the pursuit of the good life. In understanding our nature, Aristotle believes it is possible to discern what is good for humans, much like we can for animals by understanding their nature. Aristotle's view on human nature and ethics has significantly influenced Western thought and remains relevant in discussions about the nature of human behavior.