Final answer:
Aristotle viewed the rule of law as the most crucial principle for a successful democracy, acting as a safeguard against the potential self-interest of the majority.
Step-by-step explanation:
Based on the provided texts, Aristotle believed that the rule of law was the most important principle for a successful democracy. While he acknowledged the ideal would be rule by a virtuous ruler or rulers (monarchy or aristocracy), he recognized the dangers of tyranny and oligarchy. Therefore, he considered democracy, particularly one where the middle class holds power and political offices that reflect various levels of wealth, could work towards securing the public good if it had great respect for the rule of law. This would prevent the majority from ruling solely in their own interest at the expense of the minority.
Consequently, the answer to which political principle Aristotle believed was most important for a successful democracy is B. the rule of law.