Natural monopolies are to market efficiency as public goods are to what?

Natural monopolies are companies that can provide a service more efficiently than multiple competitors, often because they require large investments in infrastructure, like water or electricity. In contrast, public goods are resources that everyone can use without depleting them, such as clean air or national defense. While natural monopolies focus on efficiency in providing goods or services, public goods highlight the importance of accessibility and shared benefit. For example, a natural monopoly might be a utility company that supplies water to a city, while a public good would be a park that everyone can enjoy without paying a fee. Both concepts highlight different challenges in economics: one about efficient service delivery and the other about ensuring everyone has access to essential resources.