Document ID: ./input/supremecourt_opinions/opinions/21pdf/20-1530_n758.pdf
Page Number: 63

Cite as:  597 U. S. ____ (2022) 

7 

KAGAN, J., dissenting 

(here, fossil-fuel-fired power plants) and the relevant pollu-
tant (here, carbon dioxide) an emission level—more partic-
ularly, 

“the degree of emission limitation achievable through 
the application of the best system of emission reduction 
which  (taking  into  account  the  cost  of  achieving  such
reduction and any nonair quality health and environ-
mental impact and energy requirements) the [EPA] Ad-
ministrator  determines  has  been  adequately  demon-
strated.”  §7411(a)(1). 

To take that language apart a bit, the provision instructs
EPA to decide upon the “best system of emission reduction
which . . . has been adequately demonstrated.”  The provi-
sion  tells  EPA,  in  making  that  determination,  to  take  ac-
count of both costs and varied “nonair” impacts (on health, 
the environment, and the supply of energy).  And the provi-
sion finally directs EPA to set the particular emissions limit 
achievable through use of the demonstrated “best system.” 
Taken as a whole, the section provides regulatory flexibility 
and  discretion.  It  imposes,  to  be  sure,  meaningful  con-
straints: Take into account costs and nonair impacts, and
make sure the best system has a proven track record.1  But 
the core command—go find the best system of emission re-
duction—gives broad authority to EPA.

If that flexibility is not apparent on the provision’s face, 
consider  some  dictionary  definitions—supposedly  a  staple
of this Court’s supposedly textualist method of reading stat-
utes.  A “system” is “a complex unity formed of many often
diverse parts subject to a common plan or serving a common
purpose.”  Webster’s  Third  New  International  Dictionary 
2322  (1971).  Or  again:  a  “system”  is  “[a]n  organized  and 

—————— 

1 Those constraints have had real effect: They have led EPA in prior
rulemakings to exclude a number of pollution-control measures from the 
“best system of emission reduction.”  See Brief for United States 49 (col-
lecting citations).