The Defective Unopened Drum of Paint

The operative substantive law sometimes can be understood only by understanding the actual, as opposed to the ostensible, rules of relevance that define it.

The material issue appears to be whether the second drum of paint is defective. On that issue the evidence that the first drum was defective is hardly probative. Before concluding that the second drum is defective, one would want to know at least whether the first drum caused the roof leaks and, if so, why? Was there a defect in the paint formula, poor ingredients, or an error in preparation, handling, or storage? Without more information on these points, is it sound to conclude that because the first drum may have been bad, the second drum is bad? Does it seem more likely that D would customarily sell bad paint under a ten-year warranty or that it occasionally sells a bad drum? Certainly if a dissatisfied buyer must prove that her can of paint is defective in order to prevail, the offered evidence would not be sufficient for the plaintiff to survive a motion for a directed verdict.

Yet even if D showed that the second drum came from an entirely different batch of paint, this plaintiff might still win. How could this be so? If P wins, the court could be generating a new substantive rule of law that when a customer has been harmed by a defect in a company's warranted product, the customer can get her money back on all similar products that she had purchased prior to notice of the product failure. The theory on which this new rule of substantive law might be based is that the company breached not only its product warranty but its trust relation to that customer, a relationship that would only be reestablished if the customer were to make a further purchase after she became aware of the defect in the first can of paint.

Thus, if the issue is whether the second drum is bad, the evidence in question is of tenuous value. But if the issue is whether P should get her money back regardless of whether the second drum is good or bad, so long as she bought the second drum before her roof started leaking and after applying paint from the first drum, the offered evidence is very probative. Understood on this basis, a subtle, but undoubtedly substantive, rule of law is revealed behind what would otherwise be a doubtful evidentiary ruling. Once the new substantive rule is recognized, the relevance question is easy; indeed, they are one and the same thing. The concept of relevance defines the substantive concept, and vice versa.