Document ID: ./input/supremecourt_opinions/opinions/21pdf/20-1410_1an2.pdf
Page Number: 26.0

6 

XIULU RUAN v. UNITED STATES 

ALITO, J., concurring
ALITO, J., concurring in judgment 

more obvious that Congress did not cast the “except as au-
thorized” introductory proviso as an element of distributing
or dispensing a controlled substance.

Instead,  that  proviso  clearly  creates  an  affirmative  de-
fense—that  is,  a  “justification  or  excuse  which  is  a  bar  to
the imposition of criminal liability” on conduct that satisfies 
the elements of an offense.  1 W. LaFave, Substantive Crim-
inal  Law  §1.8(c)  (3d  ed.  2018).  Section  841(a)(1)  has  two
main parts: a principal clause generally prohibiting “know-
ingly or intentionally” doing certain things with respect to 
controlled  substances  (i.e.,  manufacturing  them,  distrib-
uting them, etc.), and a proviso indicating that these acts 
are unlawful “except as authorized” by other statutory pro-
visions.  As  we  have  long  held,  the  default  rule  for  inter-
preting provisions with this structure is that “ ‘an exception 
made by a proviso or other distinct clause’ ” designates an 
affirmative  defense  that  the  Government  has  no  duty  to 
“ ‘negative.’ ”  Dixon, 548 U. S., at 13 (quoting McKelvey v. 
United  States,  260  U. S.  353,  357  (1922));  see  also  United 
States v. Dickson, 15 Pet. 141, 165 (1841) (calling this “the 
general  rule  of  law  which  has  always  prevailed”).    When 
this rule applies, it is “ ‘incumbent on one who relies on such 
an exception to set it up and establish it.’ ”  Dixon, 548 U. S., 
at 13 (quoting McKelvey, 260 U. S., at 357).

The  CSA  explicitly  incorporates  this  default  rule.  As 
noted,  §885(a)(1)  provides  that  the  prosecution  need  not
“negative  any  exemption  or  exception  set  forth  in  this  sub-
chapter in any complaint, information, indictment, or other
pleading or in any trial, hearing, or other proceeding.” (Em-
phasis  added.)  Short  of  using  the  words  “affirmative  de-
fense,” there is no clearer way of indicating that authoriza-
tion constitutes an affirmative defense. 

On the most natural reading, then, §841(a)(1) creates an 
offense that has as its elements (1) knowingly or intention-
ally  (2) distributing  or  dispensing  (3) a  controlled  sub-
stance.  The “[e]xcept as authorized” proviso recognizes an