What reasons might one have for not voting? Ineligibility: it could be that someone would like to vote but, for whatever reason, does not qualify as a voter. Physical incapacity: someone may want to vote but be unable to get to a voting booth or fill out his ballot, etc. Mental incapacity: one may be eligible to vote but, due to some considerable ailment or illness, not be of right mind.
A more interesting reason would be that someone claims to be indifferent. Perhaps, when asked, the person says that he can’t see any difference (in substance or consequence) between the candidates; or that all politicians, e.g., are corrupt or ineffectual or whatever; or that he can’t make out how his vote, counting only for 1, ‘matters’ overall. Or perhaps he feels good and alienated from his fellows such that he can’t see himself as belonging to one group or another unless ‘belonging to some group’ translates into being, say, a member of a band.
The indifferent person above is reminiscent of a rebel, a towheaded dissident, a rebellious youth. Suppose, though, after growing up some and learning a thing or two about the world, he were to say that he is not indifferent to voting per se but that he does not believe that liberal democracy has any moral legitimacy. (Maybe he scrunches his nose at Right Hegelianism.) Then his not voting could be counted (so to speak) as a form of abstention.
We need to examine what it means to vote or, really, to take a test of any kind. When I take a particular test, I am measuring my performance against some standard already set by this test. At the same time, however, I am testing the ability of this particular test to stand as a standard against which I measure a certain ability. It is possible that this test is not, as we say, an accurate depiction of my ability to do whatever it is that the test is said to be testing. To clarify things, let’s call the first test that of my performance and the second test that of its validity.
The third test of any test is the legitimacy of the system to pose as a system in which my performance is tested and the validity of this test is reasserted. Any time I take, e.g., the SAT I am tacitly throwing my weight behind the idea that the system in which the SAT is offered is legitimate. Yet if I do not take the SAT because I reject its claim to legitimacy, then I can be said to be abstaining in some more robust sense.
By analogy, any vote I cast tests my performance (as a good voter), the validity (of, say, this kind of voting apparatus), and the legitimacy of voting as a practice on behalf of the State. I may decide not to vote because I may not believe in the modern conception of politics that goes by the name of liberal democracy. Abstention, one hopes, would not (just) be No to this type of politics but rather Yes to some other form such as anarchism, civic humanism, direct democracy, or (in my case) revolutionary Aristotelianism.