Comment by milesrout

Here are two examples.

First, a made up but illustrative one. The statute says something vague like "a term in a standard form consumer contract that is oppressive or unconscionable is void." In a common law system (anything derived from English law, including US, Australia, etc) the meaning of these terms, if they aren't defined elsewhere in the statute, is figured out based on decided cases. Someone will argue that it covers a particular clause, and the judge will decide if it does. The judge might give a detailed test for what constitutes "oppressive" or might reuse an existing one from a different context or whatever. The decision might be appealed and a panel of judges decide the meaning. But over time, and as cases are decided, the meaning becomes clear. You can point to half a dozen examples of clearly oppressive clauses and a dozen that clearly aren't, there is a legal test for what counts, etc. The law develops towards certainty and the doctrine of precedent also means it stabilises: it isn't going to change its meaning just because new judges are appointed, because they generally follow precedent pretty closely.

Under the Chevron doctrine, there is an extra step. If a government agency says that its interpretation is that "oppressive" means X, then if that interpretation is reasonable, if it is open on the wording of the statute, then the inquiry stops there. The court defers to the government agency. This has the benefit, admittedly, that the definition can change over time according to changing conditions. But it has downsides. It is giving the job of deciding what laws mean to the government, rather than the judiciary. The government is meant to act according to law, not to interpret it. That isn't the executive's proper function. But quite apart from the philosophical objections, it is no good for stability. A new government is elected and the official interpretation changes. This happens a lot. A new government is elected and it is decided that now "restraint of trade" clauses in employment contracts are legal. Four years later they're unenforceable. Four years layer they're enforceable again. No laws changed, no regulations are passed, a government agency just releases a new statement of its official interpretation of the law.

That is quite different to, e.g., there being a statute saying "terms in consumer contracts must accord with the regulations promulgated by the department of consumer protection as in force at the date of execution of the contract" because:

1. It is clear what is delegated to the executive and what is not.

2. It is clear that the definition applied is the definition at the time the contract was signed, and the "interpretation" is not retrospective.

3. It is still up to the court to give a clear, consistent, precedential ruling as to the meaning of the regulations themselves.

This example is real: Chevron itself. There, the EPA changed the definition of "source" of air pollution, without Congressional approval, so that "source" was much narrower (making pollution harder to regulate).