Document ID: ./input/supremecourt_opinions/opinions/17pdf/16-1454_5h26.pdf
Page Number: 39.0

Cite as:  585 U. S. ____ (2018) 

15 

BREYER, J., dissenting 

want to accept those cards that many customers have and 
use.  Ibid.  From this, the majority concludes that “courts
must  include  both  sides  of  the  platform—merchants  and 
cardholders—when  defining  the  credit-card  market.” 
Ante, at 12; accord, 838 F. 3d, at 197. 

1 
Missing from the majority’s analysis is any explanation 
as  to  why,  given  the  purposes  that  market  definition 
serves in antitrust law, the fact that a credit-card firm can 
be  said  to  operate  a  “two-sided  transaction  platform”
means  that  its  merchant-related  and  shopper-related 
services  should  be  combined  into  a  single  market.    The 
phrase  “two-sided  transaction  platform”  is  not  one  of 
antitrust  art—I  can  find  no  case  from  this  Court  using
those words.  The majority defines the phrase as covering
a business that “offers different products or services to two 
different  groups  who  both  depend  on  the  platform  to  in­
termediate  between  them,”  where  the  business  “cannot 
make a sale to one side of the platform without simultane­
ously  making  a  sale  to  the  other”  side  of  the  platform. 
Ante, at 2.  I take from that definition that there are four 
relevant  features  of  such  businesses  on  the  majority’s 
account: they (1) offer different products or services, (2) to
different  groups  of  customers,  (3)  whom  the  “platform”
connects, (4) in simultaneous transactions.  See ibid. 

What  is  it  about  businesses  with  those  four  features 
that  the  majority  thinks  justifies  a  special  market-
definition  approach  for  them?    It  cannot  be  the  first  two 
features—that  the  company  sells  different  products  to 
different groups of customers.  Companies that sell multi­
ple  products  to  multiple  types  of  customers  are  common­
place.  A  firm  might  mine  for  gold,  which  it  refines  and 
sells  both  to  dentists  in  the  form  of  fillings  and  to  inves­
tors in the form of ingots.  Or, a firm might drill for both 
oil  and  natural  gas.    Or  a  firm  might  make  both  ignition