Does the decision of the US Supreme Court have to be unanimous?
The Supreme Court requires only a simple majority vote to decide a case: If all nine justices are present, five of the nine must agree. The Court must have a quorum of six justices to hear a case.
YES, depending on the term. For the Court
terms 2002-2014, Slate's Eric Posner reports that the Supreme Court
handed down unanimous decisions in about half the cases they
decided, while close 5-4 decisions were about 20% of the decisions.
Fragmentation on the Supreme Court (close 5-4 decisions) was higher
in the 1980's and before, but since about 1995 the fragmentation
has been decreasing.
YES. Over the last sixty years, unanimous decisions have been almost TWICE as common as close 5-4 decisions. In the Roberts Court (2005 - present), unanimous decisions have been delivered by the Court in about half the cases decided. Reported by Slate's Eric Posner (Professor of Law at University of Chicago), and brenbarn.net