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Page Number: 44

20 

OHIO v. AMERICAN EXPRESS CO. 

BREYER, J., dissenting 

economists  do.  As  the  economists  who  coined  the  term 
explain, if a “two-sided market” meant simply that a firm 
connects two different groups of customers via a platform, 
then  “pretty  much  any  market  would  be  two-sided,  since
buyers and sellers need to be brought together for markets
to  exist  and  gains  from  trade  to  be  realized.”    Rochet  & 
Tirole,  Two-Sided  Markets:  A  Progress  Report,  37  RAND 
J.  Econ.  645,  646  (2006).    The  defining  feature  of  a  “two-
sided market,” according to these economists, is that “the
platform can affect the volume of transactions by charging 
more to one side of the market and reducing the price paid 
by  the  other  side  by  an  equal  amount.”    Id.,  at  664–665; 
accord,  Filistrucchi  299.  That  requirement  appears  no­
where  in  the  majority’s  definition.    By  failing  to  limit  its
definition  to  platforms  that  economists  would  recognize 
as “two sided” in the relevant respect, the majority carves 
out  a  much  broader  exception  to  the  ordinary  antitrust
rules than the academic articles it relies on could possibly 
support.

Even  as  limited  to  the  narrower  definition  that  econo­
mists  use,  however,  the  academic  articles  the  majority
cites  do  not  support  the  majority’s  flat  rule  that  firms 
operating “two-sided transaction platforms” should always
be  treated  as  part  of  a  single  market  for  all  antitrust 
purposes.  Ante, at 13–15.  Rather, the academics explain
that  for  market-definition  purposes,  “[i]n  some  cases,  the 
fact that a business can be thought of as two-sided may be
irrelevant,”  including  because  “nothing  in  the  analysis  of
the  practices  [at  issue]  really  hinges  on  the  linkages  be­
tween  the  demands  of  participating  groups.”   Evans  & 
Schmalensee,  Markets  With  Two-Sided  Platforms,  1  Is­
sues in Competition L. & Pol’y 667, 689 (2008).  “In other 
cases,  the  fact  that  a  business  is  two-sided  will  prove 
important both by identifying the real dimensions of com­
petition  and  focusing  on  sources  of  constraints.”    Ibid. 
That  flexible  approach,  however,  is  precisely  the  one  the