Final answer:
The legal rule 'evidence which is not relevant is not admissible' expresses a conditional relationship and is true.
Step-by-step explanation:
The legal rule, 'evidence which is not relevant is not admissible,' expresses a conditional relationship. This statement is true. Relevance is a key requirement for evidence to be admissible in a court of law. If evidence is not relevant to the case, it cannot be admitted as it does not help establish the truth or falsehood of the facts in question.