What are the grounds of a state's
authority? Why do most of us think that the state can tell us what to do? If we are not going to be
anarchists, either
political or
philosophical, then we want to find some basis for our acceptance of state commands.
One such basis is consent theory. This says that the authority of the state is grounded on consent by the governed. Real states have been constructed to satisfy this influential idea, with people asked to vote on a founding constitution. The theory has had a real and lasting influence more than almost any other theory of political obligation. But it is complete rubbish. Nevertheless, it's rubbish everyone should know about. Even though the theory fails, it's kind of a gold standard for legitimacy - other theories are measured up to it or are created as responses to it. And for this reason it's very important. I'm a politics geek, though, so don't take my word for it...
Consent theory says that at some point in their lives citizens signal their consent to the regime under which they live. Government reflects the will of the people etc. This sounds plausible, but think about it - when did you last fill in a regime consent form?
Consent theory is closely tied in with social contract theory (same thinkers - Locke, Rousseau, Hobbes - and social contract theory is a type of consent theory). Both have as their starting point theories about the State of Nature. For Locke, in his Two Treatises of Government the state of nature is a situation of perfect freedom and equality. Persons in this state have rights against one another, which are natural rights. A right of this sort is a right to the exclusive use of something - I have a right to the bag I have made, as I have mixed my labour with it, and no one else can use it without my permission. Similarly, my rights to life, liberty, bodily integrity etc. are rights I hold against other people, as well as rights to the things themselves. Your right to move your fist ends at my face.
In a state of nature Locke has me as the master of my own domain. In order to leave this situation we must have had to do something to put ourselves under obligation to a state. Duties are basic moral requirements we have regardless of anything we've undertaken, but in order to have on obligation, one has to perform some specific act, and the obligations we incur create correlative rights, by being incurred towards some specific person, institution or set of institutions (such as the state). For consent theorists, we have incurred these obligations to the state by our consent to the state. We have some reason to leave behind the state of nature (if we were Hobbesians, we'd have a lot of reason) and because of that we consent to the rule of the state.
All theories of legitimacy rest on two distinct claims. The first of these is at the level of moral principle, a theory of how the state's rights are gained. The second is at the level of practical application, which says that there are some states to which the theory actually applies. Now at the level of principle consent theory works fine. It's very admirable in fact, because there could be nothing more legitimate than something to which we've given full consent. However, at the level of application it's a miserable failure. We simply don't consent to the rule of the state. Not directly, anyway.
One solution to this pretty fundamental problem is to say that, while we do not give direct consent, we give tacit consent through certain of our actions. For instance, by voting in elections, or even by using state highways, we have consented to the regime we live under. This idea rests on the claim that we could always emigrate if we did not consent to the state. However, this just isn't realistic, and particularly was not in the past, when travel was so expensive. But it is not simply the financial cost which makes such moves prohibitive - it is the emotional cost and the fear that there would be nothing better. Tacit consent may be okay as a theory, but it can't be this extensive - not everything we do can be taken as a sign of our consent, even if in practice we would consent to state rule if asked. Our sign must be fully deliberate and fully voluntary.
Most of us do believe intuitively that the state is legitimate and try to accept consent theory in some form as an explanation for why we believe it. Others have tried to think up schemes under which we would actually consent, but these are impractical and required detailed thinking regarding how often we would have to consent in order to be considered obligated to obey. Meanwhile, you may continue to vote and think of this as an act of consent, but remember that among you are the anarchists, undermining your theory all the time - voting only to cut their losses and biding their time until the revolution!