Contracts themselves are not articles of contract law. - This is true, but the concept of inheritance holds.
'Illegal' ~ 'against the law'. What is doing something against the law? Doing something the law states you are not allowed to do. So in practice under continental law (Napoleonic / Germanic) a law states "do X" or "leave Y" and doing the opposite is illegal. Then, if the law states "you must (under good faith) fulfill your contract" and you do not fulfill your contract ... that's illegal. A legally binding contract has the force of law for the signing parties.
> Contracts themselves are not articles of contract law. - This is true, but the concept of inheritance holds.
Of 'inheritance'? What does this mean? Are you trying to apply the rules of OOP to contract law, as if an individual contract were an instance of contract law...?
Yeah I was trying to make an argument the target audience might find persuasive. Inheritance is a nice concept when reasoning about (continental) contracts since a contract is only a contract if and only if it abides by contract law. That's a strict inheritance there. In truth, it's a bit more flexible: a contract could still be a contract if there are illegal provisions in the contract since at first only the illegal provisions will be scrapped by a judge.
> a contract is only a contract if and only if it abides by contract law
That's true, but I don't quite see how that makes a contract the law. Someone who doesn't turn up to work isn't doing something illegal by dint of breaking their employment contract. IME, 'illegal' generally refers to breaking the criminal law, whereas I wouldn't say this even breaks civil law, sensu stricto. https://malesculaw.com/is-breach-of-contract-a-tort/
That does not follow trivially. Contracts themselves are not articles of contract law.