Democracy requires a demos but the demos can’t be determined democratically. Non-democratic solutions fail to adequately explain why current political boundaries should be the way they are. The inability to properly account for who the people ought be raises other challenges to democracy’s coherence and claims of legitimacy. This has become know as the Boundary Problem.
The Boundary Problem is really three distinct but interconnected problems. The first of these, what we might call the justification problem, is that a democracy cannot determine who should be a member of it democratically. Any attempt to justify the inclusion of some people but not others within the demos will either be circular or result in an infinite regress because who the people are is a matter logically and temporally prior to how they might decide. The circularity of a demos determining its own make up is obvious - a determinate group of people can’t choose to create themselves democratically because any democratic act of a people requires that people to already exists.
What may not be so obvious however, is the regress that results when one people attempt to alter themselves democratically. Why can’t a people can’t vote or deliberate on who should be included - the UK might deliberate on Scottish secession or Crimea could hold a referendum on a union with Russia for example - because clearly they can and often do. But this just raises an earlier question of who should participate in this process. This of course could be answered by a prior vote or deliberation but who gets to vote or deliberate on this? An infinite regress of who gets to vote on who gets to vote means the inclusion of the first people cannot be addressed democratically.
Non-democratic accounts of who the people ought to be are similarly problematic. Whether the criterion of inclusion is descriptive - nationality, linguistic, cultural, or economic salience, or geographic proximity for example - or more normative such as consent or the principle of all affected interests, we are left with the worrisome realisation that there are no satisfactory accounts for the fundamental question of who ought make up the demos.
The lack of justification for who the people ought be raises two more derivative problems concerning contradiction with democratic principles and the undermining of democratic attempts to legitimate the authority of the state. What we might call the value problem arises when arbitrary methods of determining the demos conflict and contradict with core democratic values. The most fundamental of these is the principle of self-determination and self-rule. Failure to properly define the people, and the subsequent over or under enfranchisement of a political association results in a state of heteronomy, the political subjugation of one group by another.
The justification problem also raises another challenge, what we might call the predetermination problem. This stems from the fact that the logical and temporal priority of the who over the how results in the who having a fundamental impact on the how. Who participates in any democratic process it critical in determining the outcome of it; and given sufficient polarity and clustering of agent preferences and values across any political space, the question of inclusion fully predetermines the outcome of any democratic mechanism. And when the basis of democracy’s legitimising claims rest the difference making qualities of democratic processes, then the predetermination of outcomes renders these difference making and legitimising claims vacuous.