Distinguish a public good from a private good in terms of excludability and rivalrous consumption.

• A. Public goods are non-excludable and non-rivalrous; private goods are excludable and rivalrous.
• B. Public goods are excludable and rivalrous; private goods are non-excludable and non-rivalrous.
• C. Public goods are excludable but non-rivalrous; private goods are non-excludable and rivalrous.
• D. Public goods are rivalrous and excludable; private goods are non-rivalrous and non-excludable.

Answer: (A)

Excludability and rivalry in consumption determine whether a good is public or private. A public good is non-excludable and non-rivalrous: once provided, you can’t reliably prevent others from using it, and one person’s use doesn’t reduce another’s ability to use it. Private goods are excludable and rivalrous: providers can prevent non-payers from consuming them, and each unit consumed reduces the amount available for others. So the statement that public goods are non-excludable and non-rivalrous while private goods are excludable and rivalrous matches the standard distinction. The other descriptions would imply you could exclude users or that one person’s use would diminish others’ consumption for public goods, which isn’t correct.