True. Clarity of any law should be absolute. But even while a law is framed, a lot of discussions, points, counter points etc., are analysed and taking in to consideration all these, a wholistic view developed on the basis of which the law is evolved.
But we know who make the law. In specific laws, we also know how those people could be impacted by the very law that they make. In such cases, there is every possibility that things are left ambiguous.
Here is where the judicial system comes into play to interpret it. This is the most crucial part. Such interpretation should be by uninterested party, who is of impeccable character, honest and having the interest of the society at large. If an ambiguous law is interpreted by such a person, one can expect a fair interpretation. That's why selection of judicial officers is a very very tricky issue.
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They both are legal terms to the best of my knowledge. Law is written and defined very ambiguously. One lawyer interprets a law, the other challenges for the clarity of that law. I think that discussion is necessary. But the justice is done by the judge, who has to answer at the end.