Business rules should be:

Business rules are best understood as foundational guidelines that govern the behavior of systems and organizations. When they are referential throughout the use cases, it means that these rules are consistently applied and referenced in various scenarios, making them integral to the decision-making process and operational consistency.

Incorporating business rules into use cases ensures that all stakeholders have a common understanding of the criteria that dictate the business processes. This not only enhances clarity but also helps in identifying any discrepancies in system behavior versus expected outcomes. By having business rules be referential in use cases, it supports better communication, helps in maintaining alignment between the business objectives and the system functionalities, and fosters accountability among teams.

As for other options, general guidelines that apply universally might not account for specific contexts or nuances within different business scenarios. Theoretical business rules devoid of practical implications can lead to confusion and ineffective implementation. Finally, relying solely on verbal communication for important business rules can result in misinterpretations and a lack of formal documentation, which is crucial for clarity and consistency in business operations.