One could make a colorable argument that SCOTUS cases decided by one vote are the most important decisions of the Court. One could also argue that unanimous opinions are either the most or least important decisions.

Unanimous decisions require the cohesion of all of the justices from both sides of the ideological aisle. With such polarization on the Court, unanimity dipped to a decade low this past term. Under such constraints, majority authors can only gain acceptance from the other justices by writing in a way that doesn’t offend any other justices’ views. On the other hand some argue that unanimous opinions lack dissenting votes because they deal with neutral issues, ones that lack great complexity, or cases where decisions have easy answers. 

There is a norm on the Court that justices write approximately the same number of majority opinions for each oral argument sitting (month) and across each term.  Since only some of the justices are in the majority in contentious decisions, unanimous opinions are often given to justices who don’t author more contentious decisions because they need to fill their opinion slate with opinions in which they are in the majority. This is why the authors of unanimous opinions also tend to be in the Court’s majority least frequently.

The top five unanimous decision authors since 1946 are:

• Marshall – 161
• Stevens – 155
• White – 146
• Rehnquist – 145
• Douglas – 142

The most from a current justice is Thomas with 114

If we look at the justice’s percentage of unanimous opinions out of all of their opinions we see the following:

• Sotomayor – 51.1%
• Kagan – 50.6%
• Marshall – 50.0 %
• Souter – 49.4%
• Thomas – 49.1%
• Ginsburg – 49.1 %

An interesting facet of the percentages is that **three of the top six justices (and the top two overall) are female**. All justices on the percentage list are liberal which says something about ideology, but what does this say about the role of gender in opinion assignment? An interesting topic for further research…

As for cases decided by one vote, these are typically the toughest majority coalitions to sustain. Especially during periods with ideological intensity, a justice would have to pull together all justices from one side of the ideological spectrum to cobble together typically five votes.

The top justices with decisions by one vote since 1946 are

• Rehnquist – 97
• White – 94
• Kennedy – 93
• Brennan – 82
• Stevens – 66

The most from a current justice is from Thomas with 41

If we look at the percentage of one vote from all decisions over the same period we find

• Kennedy – 33.7%
• Kavanaugh – 29.2%
• R. Jackson – 28.9%
• Gorsuch – 27.8%
• Reed – 27.6%

Kennedy, the swing justice for well over a decade is in the top spot by a wide margin. Two current justices, Gorsuch and Kavanaugh, have had heavy loads of close decisions so far. In a few years we will be able to better judge if these percentages will sustain themselves or if they merely relate to the short time these justices have sat on the Court.