Final answer:
Source 1 highlights the spread of Enlightenment ideas as a cause of the French Revolution, while Source 3 emphasizes immediate economic crises and class issues driving revolutionary movements.
Step-by-step explanation:
One major difference between Source 1 and Source 3's interpretation of the causes of the French Revolution is that Source 1 mentions the spread of 'philosophic' ideas, while Source 3 highlights revolutionary impulses. Source 1 aligns with Enlightenment thinking and the influence of philosophes such as Rousseau, Diderot, and Voltaire, which questioned traditional ways of thinking and proposed ideas of social and legal equality.
On the other hand, Source 3 suggests that the French Revolution was driven by more immediate factors such as economic crises, including famine and the near-bankruptcy of the French Crown, combined with the Enlightenment rhetoric inspiring the middle class to demand political power, which resulted in revolutionary movements.