Horizontal Accountability - A Normative Principle of Democracy

In framing their 8 dimensions of democracy, Diamond and Morlino include horizontal accountability as a key, necessary element of testing how strong a democracy is. As with the other dimensions, horizontal accountability is an activity which can be monitored and, potentially, measured. My objective in this exploration is to present horizontal accountability as a normative requirement of democracy, a requirement that must exist if we are to consider democracy as a qualitative concept.

To clarify what I mean by ‘accountability’. It must be useful enough to convey meaning, but broad enough to avoid the details of what we judge and what metrics we use to judge. How well horizontal accountability works as an empirical activity, important as it is, is not a focus here.

A useful starting point in understanding what we mean by ‘horizontal accountability’ is to use a definition such as “Accountability is a relationship between an actor and a forum, in which the actor has an obligation to explain and to justify his or her conduct, the forum can pose questions and pass judgement, and the actor may face consequences” (Bovens 2007, p. 451). This provides a framework, useful across different versions of accountability. ‘Actors’ is being used as a device to capture individual or group actions. Similarly, ‘forum’ is being used as a device to capture individual or group judgement. There is a power relationship between the actor and forum. That relationship is one in which the forum has the power to instruct the actor to act in a legally defined manner.

On first look, this may look suspiciously like vertical accountability. Vertical accountability describes the relationship between citizens and their government: forum and actor. The electorate agrees, however that is processed, that the government can act on its behalf. The relationship is delegated (Walsh, 2020, p. 1). In respect of horizontal accountability, both the actor and the forum are state bodies charged with specific duties and oversight. They do not delegate to each other but they do have the power to pass judgement on each other. They serve as “the checks and balances… used by the legislative and judicial branches of government to hold the executive accountable” (Walsh, 2020, p. 1).

As Mechkova, Lührmann and Lindberg (2019, pp. 55–57) demonstrate, horizontal accountability is institutionally demanding: it tends to emerge only once vertical accountability is robust and civil society is sufficiently developed to support transparency and information flows. This sequencing is itself normatively significant. Where those prior conditions are absent or weak, horizontal accountability remains underdeveloped and that absence has democratic cost. Delegated authority goes unchecked, executive power may be unconstrained and the rule of law, a key normative democratic element itself, is subject to compromise. The empirical pattern of late emergence reinforces, rather than undermines the normative case. It reveals horizontal accountability as a condition that democracies must work towards (Mechkova, Lührmann and Lindberg, 2019, pp. 57–59). Without it, the conditions for being able to assess the quality of democracy are unlikely to be present.

A recent example may help to clarify the horizontal relationship without relying on empirical judgements. In 2026, the Office for Environmental Protection (OEP) reported on legal proceedings against the Department for Environment, Food and Rural Affairs (Defra) and the Environment Agency (EA). OEP alleged that Defra and EA had failed to comply with the Water Framework Directive (WFD) Regulations (OEP, 2026). The significance of this example does not lie in the outcome, the case is ongoing, but in its accountability structure. A state body triggered judicial scrutiny of another state body. The OEP, EA and Defra are state bodies with legally defined mandates. The OEP does not derive its authority from Defra or EA, nor does it delegate power to it. Instead, it exercises an independent statutory capacity to question and challenge the conduct of another public institution. The forum in Bovens’ sense is the court, which has authority to require explanations, assess legality and impose consequences. This is horizontal accountability: a state institution triggering scrutiny of another state institution, with judgement rendered by a third. No citizens, interest groups or elections are involved to force actions. The relationship is internal to the state, yet normatively essential to the quality of democracy because it applies the rule of law and constrains executive power. Democracies require institutionalised state bodies capable of scrutinising, investigating and sanctioning other state bodies. Without such horizontal accountability, delegated authority risks becoming arbitrary authority (O’Donnell, 1998, p. 119).

Horizontal accountability is therefore not an optional institutional refinement but a constitutive element of democratic rule. Without legally empowered state bodies capable of scrutinising and constraining one another, the delegation of authority from citizens to government would lack meaningful safeguards.