The plurality opinion stated that it was upholding what it called the "essential holding" of Roe.
Therefore, the concurring opinion joined by the greatest number of judges is referred to as the plurality opinion.
It is important to note that there were two opposing 4-person plurality opinions and then Justice Powell's.
Arguing that the entire law was unconstitutional, these two Justices described the plurality opinion as "adrift."
The 1980 ruling was a plurality opinion without a majority rationale, and many lower courts had applied it in only a very limited way.
An example of a case decided by a plurality opinion is Hamdi v. Rumsfeld.
The plurality opinion gives some guidance on when an intermediate warning should be considered to be effective.
Thus the plurality opinion was not controlling, and the conviction of the lower court was affirmed.
The Court's plurality opinion left the precise reasoning for the decision unclear.
A key 1958 plurality opinion, Trop v. Dulles, makes just that point.