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16 

DEPARTMENT OF HOMELAND SECURITY v. 
REGENTS OF UNIV. OF CAL. 
Opinion of the Court 

n. 6 (1969) (plurality opinion).  See also post, at 5.  Proce-
dural requirements can often seem such.  But here the rule 
serves important values of administrative law.  Requiring 
a  new  decision  before  considering  new  reasons  promotes 
“agency accountability,” Bowen v. American Hospital Assn., 
476 U. S. 610, 643 (1986), by ensuring that parties and the
public  can  respond  fully  and  in  a  timely  manner  to  an 
agency’s exercise of authority.  Considering only contempo-
raneous  explanations  for  agency  action  also  instills  confi-
dence that the reasons given are not simply “convenient lit-
igating  position[s].”  Christopher  v.  SmithKline  Beecham 
Corp., 567 U. S. 142, 155 (2012) (internal quotation marks
omitted).    Permitting  agencies  to  invoke  belated  justifica-
tions, on the other hand, can upset “the orderly functioning 
of the process of review,” SEC v. Chenery Corp., 318 U. S. 
80,  94  (1943),  forcing  both  litigants  and  courts  to  chase  a
moving target.  Each of these values would be markedly un-
dermined were we to allow DHS to rely on reasons offered 
nine months after Duke announced the rescission and after 
three  different  courts  had  identified  flaws  in  the  original 
explanation.

JUSTICE  KAVANAUGH  asserts  that  this  “foundational 
principle  of  administrative  law,”  Michigan,  576  U. S.,  at 
758, actually limits only what lawyers may argue, not what
agencies may do.  Post, at 5.  While it is true that the Court 
has often rejected justifications belatedly advanced by ad-
vocates, we refer to this as a prohibition on post hoc ration-
alizations, not advocate rationalizations, because the prob-
lem is the timing, not the speaker.  The functional reasons 
for  requiring  contemporaneous  explanations  apply  with 
equal  force  regardless  whether  post hoc  justifications  are 
raised in court by those appearing on behalf of the agency
or  by  agency  officials  themselves.   See  American  Textile 
Mfrs. Institute, Inc. v. Donovan, 452 U. S. 490, 539 (1981) 
(“[T]he  post  hoc  rationalizations  of  the  agency  . . .  cannot 
serve as a sufficient predicate for agency action.”); Overton