Since an index was an abstraction, there was no straightforward way in which an index future could be settled other than in cash. In 1968, Sullivan and two leading members of the Chicago Board of Trade consulted securities lawyer Milton Cohen about the feasibility of a Dow Jones futures contract. Cohen advised against proceeding: the contract would violate Illinois law (Falloon 1998, pp. 209-210).

Donald MacKenzie, An Engine, Not a Camera, loc. 641