Background of Cold War competition.  Desire to "sell" U.S. political system.

Empirical (and desirable!) regularities of our system:

1. Only two major parties, even if some die out and others emerge.
2. Centrist parties.
3. Responsive to shifts in the electorate;  stable.
4. Non-ideological parties;  non-"membership" parties;  fuzzy platforms

Possible explanations for this happy state of affairs:  [Note the advantage of having an explanation that allows our system to be transferred to other countries.]

1. Institutional exclusion of third parties?  [Not very desirable, even if true.]
2. A culture of moderate voters (as opposed to those excitable Europeans)?  [Maybe, but this isn't transferrable.]
3. A tradition of two parties?  [Ditto]
4. The Marxist explanation that the two parties both in fact represent the owning class, but that the owning class finds it convenient to have two parties to provide the illusion (but only the illusion) of genuine political debate?  [Obviously we don't want to accept this theory, even if it were true.]
5. Downs's theory:  The happy state of affairs is due to our electoral system, which is responsive and greatly resembles a free market system.

Downs makes several simplifying, plausible assumptions:

• Electoral preferences, policy positions, and party platforms can be arranged along a single dimension (e.g., liberal to conservative;  rich to poor;  etc.).
• Parties are interested solely in winning elections.  Policy positions are merely means to that end, not ends in themselves.
• Voters are self-interested.
• Just as consumers make consumer choices among products, voters vote for the party whose position is closest to their own.

The consequences:

• There is only room for two parties.
• Parties have incentives to move to the ideological middle.
• Parties have incentives to move according to shifts in the electorate.
• Parties have incentives to obscure their differences from each other.

Problem:  There is no external standard of justice.  Whatever the individual wants (and in particular whatever the median individual wants) is what is best.  If people choose (or are forced) not to vote, this is of no concern.  If the issues are not fought out in the public arena using public reason, this is of no concern.