Document ID: ./input/supremecourt_opinions/opinions/20pdf/19-416_i4dj.pdf
Page Number: 23.0

Cite as:  593 U. S. ____ (2021) 

3 

SOTOMAYOR, J., concurring
Opinion of SOTOMAYOR, J. 

Sosa v. Alvarez-Machain.  There, the Court explained that 
it  would  “be  unreasonable  to  assume  that  the  First  Con-
gress would have expected federal courts to lose all capacity 
to  recognize  enforceable  international  norms  simply  be-
cause  the  common  law  might  lose  some  metaphysical  ca-
chet” in a post-Erie world.  542 U. S., at 730.  Indeed, while 
Erie rejected the notion of a  general federal common law, 
the  “post-Erie  understanding  has  identified  limited  en-
claves in which federal courts may derive some substantive 
law in a common law way.”  542 U. S., at 729.  For over 200 
years (both before and after Erie), courts have adhered to 
the  principle  that  “the  domestic  law  of  the  United  States 
recognizes the law of nations.”1  542 U. S., at 729. 

While Sosa refused to “close the door” to “judicial recog-
nition of actionable international norms,” it remains “sub-
ject  to  vigilant  doorkeeping.”  Ibid.  Sosa  explained  that 
“courts should require any claim based on the present-day 
law of nations to rest on a norm of international character 
accepted by the civilized world and defined with a specific-
ity  comparable  to  the  features  of  the  18th-century  para-
digms” contemplated by the First Congress (i.e., norms re-
garding  safe  conducts,  the  rights  of  ambassadors,  and 
piracy).  Id., at 725.  The Court elaborated that “the deter-
mination whether a norm is sufficiently definite to support 
a cause of action should (and, indeed, inevitably must) in-
volve  an  element  of  judgment  about  the  practical  conse-
quences of making that cause available to litigants in the 
federal courts.”  Id., at 732–733 (footnote omitted). 

In the years since, this Court has read Sosa to announce 
a two-step test for recognizing the availability of a cause of 
action under the ATS.  Courts first ask “whether a plaintiff 

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1 Other “enclaves” in which federal courts develop legal principles in a 
common-law  fashion  include,  for  example,  the  areas  of  admiralty  law, 
disputes between States, and some aspects of federal labor law.  See Col-
lins v. Virginia, 584 U. S. ___, ___ (2018) (THOMAS, J., concurring) (slip 
op., at 7).