Does the author succeed in supporting the claim that "In no other department is a thorough knowledge of history so important as in philosophy"? Yes, because he gives examples of why knowledge of history is vital to philosophy.

2.
Yes, because he proves that other departments of thought are not reliant on historical knowledge.

3.
No, because he proceeds to explain why knowledge of history is as important to other disciplines.

4.
No, because he digresses into another topic and does not address historical knowledge.