The paradox in this passage arrives when the academic study of jurisprudence is applied to English common law. The author explains how these concepts conflict.
Common law is described as an unwritten code. It is made up of traditions and ancient precedents and it is constantly changing and evolving throughout history.
The study of jurisprudence does not acknowledge the historical, evolving nature of common law. In the second paragraph, the author claims that jurisprudence interprets law as a unified system of rules that forms a logical whole. This, in comparison to the scattered, historically based tenets of common law, is the nature of the paradox.
I agree that "conflict" or "contradiction" are better words than "paradox" for describing this relationship. This may have made it more difficult for you to identify the correct answer. However, sometimes we must allow for small differences in terminology, if the answer choice matches the spirit of the passage.
The new view of the situation is provided by legal historian Peter Goodrich in the third paragraph. If you follow the order of the paragraphs, you can see why A is the correct answer.
