Final answer:
The Chief Justice of the Supreme Court writes the majority opinion if they are part of the majority; otherwise, the most senior justice in the majority assigns the role.
Step-by-step explanation:
If the Chief Justice of the Supreme Court is part of the majority, he or she gets to write the majority opinion. This is the opinion that expresses the Court's reasoning for their decision and must be agreed upon by a majority of the justices. In cases where the Chief Justice is not in the majority, the most senior justice who is in the majority gets to decide who writes the majority opinion. Alternatively, justices in the minority write dissenting opinions, and justices who agree with the majority outcome but for different reasons may write concurring opinions.