Final answer:
Public goods are non-excludable and non-rival, meaning they are accessible to all and one person's use does not impact another's ability to use them, whereas common resources may be non-excludable but can become rival in consumption if overused.
Step-by-step explanation:
Both public goods and common resources have specific characteristics in terms of excludability and rivalry in consumption. Public goods are non-excludable and non-rival, which means that it is difficult or impossible to prevent someone from using the good, and one person's use does not diminish another's ability to use it. An example of a public good is national defense; it protects all citizens regardless of individual consumption and one person benefiting from it does not reduce the protection available to others. In contrast, common resources may be non-excludable but they are often rival in consumption, meaning that one person's use can reduce the availability of the resource for others.
For example, if we consider a public park, it is non-excludable because it is available for everyone to enjoy, and it is non-rival up to a certain point where use does not significantly degrade the quality or availability of the park to others. However, when excessive use leads to congestion or damage, it can become rival in consumption. This detail is important to differentiate because common resources can be overused and depleted, whereas public goods maintain their availability regardless of individual consumption levels.