What does "vertical direct effect" allow an individual to do?

Vertical direct effect is a principle in EU law that allows individuals to invoke rights that are conferred upon them by EU directives against the state or public authorities, even if those directives have not yet been implemented into national law. This means that if a directive grants an individual specific rights, they can claim these rights directly against the state, regardless of whether the state has taken the necessary actions to incorporate those rights into national legislation.

In this context, the ability to challenge a state based solely on the provisions of an unimplemented directive exemplifies how vertical direct effect operates. It underscores the supremacy of EU law and the obligation of member states to adhere to their commitments under EU treaties. This principle is pivotal for protecting individual rights across member states, ensuring that citizens can rely on EU law directly in their legal disputes with any state authority.

In contrast, the other options do not accurately describe the function of vertical direct effect. For instance, claiming against another private individual pertains to horizontal direct effect, which does not apply to directives. Raising legal issues in any member state or challenging existing national laws more broadly involves different principles of EU law and does not specifically delineate the unique aspect of how directives can be enforced against the state directly.