A more thorough explanation:

The declaratory theory is the belief that judges' decisions do not create new laws but only serve as evidence of what the law already is. This view was held by legal scholars like Coke and Blackstone in the past, but it is no longer accepted.

There are three reasons why the declaratory theory persisted for some time after the modern English doctrine of precedent had begun to take shape:

1. It appealed to believers in the separation of powers, who did not want judges to have the power to create laws.
2. It concealed the fact that judge-made law is retrospective in its effect, meaning that it can apply to past actions.
3. When faced with a new legal question, judges tend to speak as though the answer is provided by the common law.

For example, if a court decides in December that someone is liable for their actions in January of the same year, it may appear that the court is creating a new law that applies retroactively. However, the declaratory theory would argue that the court is only stating a rule that was already in place at the time of the person's actions in January.

Overall, the declaratory theory is an outdated view of the role of judges in creating and interpreting laws.