Almost no citizen of a modern state has personally, individually signed any document agreeing to obey that state's laws, and yet most political philosophy treats citizens as genuinely bound to obey them anyway. Political philosophers generally split this deceptively simple puzzle into two related but genuinely distinct questions: legitimacy, asking what actually justifies a state's authority to make and enforce binding laws in the first place, and political obligation, asking what specifically makes any given individual citizen bound to actually obey those laws, which turns out not to follow automatically from the state's legitimacy alone.
Legitimacy is about the state's authority, not any individual's specific duty
A state's legitimacy concerns whether it has a genuine, justified right to rule and to make binding law over the people within its territory — a question that can be answered in the abstract, about the state and its institutions themselves, without yet addressing whether any particular individual citizen is personally obligated to obey. Political philosophers have offered a range of different theories of what actually grounds a state's legitimacy, including consent, actual or hypothetical; a state's success in providing genuine benefits like security and justice that its citizens couldn't easily secure on their own; and fair processes for making and changing law that a reasonable person could accept as legitimate even when they personally disagree with a specific resulting law.
Political obligation asks a further, separate question about each individual
Even accepting that a state is broadly legitimate, political obligation asks a genuinely further, separate question: what specifically makes a given individual citizen bound to obey its laws, given that they never personally, explicitly agreed to anything. Philosophers have proposed several different answers, including tacit consent, the idea that continuing to reside within a state's territory and accept its benefits implies a kind of unstated agreement to its rules, and fair play, the idea that having accepted the genuine benefits a cooperative political system provides creates an obligation to also bear its burdens, including obeying its laws, rather than free-riding on others' compliance. Each of these proposed answers faces real, serious philosophical objections — tacit consent, for instance, is criticised for treating mere residence as meaningfully equivalent to actual agreement, when in practice most people have very limited realistic ability to simply leave and live somewhere entirely outside any state's authority — which is a large part of why political obligation remains a genuinely live, unsettled question in political philosophy rather than one with a single broadly accepted answer.
What we're still unsure about
The basic distinction between legitimacy and political obligation as separate philosophical questions, and the range of proposed theories addressing each, are well documented in political philosophy scholarship. What remains genuinely, actively unsettled is whether any single theory of political obligation actually succeeds in fully justifying why a specific individual citizen is bound to obey a specific state's laws — every major proposed answer faces serious, still-unresolved philosophical objections, and some political philosophers have gone so far as to argue that no fully satisfying general theory of political obligation actually exists, a genuinely contested position within the field rather than a fringe view easily dismissed.
This sits inside Legitimacy, Authority & Political Obligation, one of seven topics in Political Philosophy, one of five domains in Philosophy, one of seventeen subjects the app can quiz you on.