Someone brings a case against some law. SCOTUS takes the case.
Four justices rule in favor of the plaintiff and hold the law should be struck down. Four justices rule to uphold the law. The ninth justice sidesteps the law's constitutionality question entirely and just rules that the case is invalid on a technicality, such as that the plaintiff didn't have standing to sue or whatever.
Obviously the law is upheld, but what's the decision? It seems weird the ninth justice gets to write it when none of the others agree. Do both of the main sides get to write a dissent?
The four who would have upheld the law concur with the result of the case, so any or all of those justices could write concurring opinions disagreeing with the 5th justice's reason for upholding the law and presenting their own reason. It would be the four who would strike the law down who would could choose (or not choose; concurrences and dissents aren't mandatory) dissenting opinions. Both the concurring and dissenting opinions could certainly be useful for future argument of the issue, but neither would have any binding authority.
