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Page Number: 38.0

14 

OHIO v. AMERICAN EXPRESS CO. 

BREYER, J., dissenting 

reason” analysis.  See also infra, at 24. 

One  critical  point  that  the  majority’s  argument  ignores
is  that  proof  of  actual  adverse  effects  on  competition  is, 
a fortiori, proof of market power.  Without such power, the
restraints  could  not  have  brought  about  the  anticompeti­
tive effects that the plaintiff proved.  See Indiana Federa-
tion  of  Dentists,  supra,  at  460  (“[T]he  purpose  of  the  in­
quiries  into  market  definition  and  market  power  is 
to  determine  whether  an  arrangement  has  the  potential 
for  genuine  adverse  effects  on  competition”  (emphasis
added)).  The  District  Court’s  findings  of  actual  anticom­
petitive  harm  from  the  nondiscrimination  provisions  thus
showed  that,  whatever  the  relevant  market  might  be,
American  Express  had  enough  power  in  that  market  to 
cause that harm.  There is no reason to require a separate
showing  of  market  definition  and  market  power  under 
such  circumstances.    And  so  the  majority’s  extensive
discussion of market definition is legally unnecessary. 

D 

The  majority’s  discussion  of  market  definition  is  also 
wrong.  Without raising any objection in general with the
longstanding  approach  I  describe  above,  supra,  at  10–11, 
the  majority  agrees  with  the  Court  of  Appeals  that  the 
market  for  American  Express’  card  services  is  special 
because  it  is  a  “two-sided  transaction  platform.”    Ante,  at 
2–5,  12–15.  The  majority  explains  that  credit-card  firms 
connect two distinct groups of customers: First, merchants
who accept credit cards, and second, shoppers who use the
cards.  Ante, at 2; accord, 838 F. 3d, at 186.  The majority 
adds that “no credit-card transaction can occur unless both 
the merchant and the cardholder simultaneously agree to
use  to  the  same  credit-card  network.”   Ante,  at  3.  And  it 
explains  that  the  credit-card  market  involves  “indirect
network effects,” by which it means that shoppers want a
card  that  many  merchants  will  accept  and  merchants