In economics, a public good
is a good that is both non-excludable and non-rivalrous in that individuals cannot be effectively excluded from use and where use by one individual does not reduce availability
to others. Gravelle and Rees: "The defining characteristic of a public good is that consumption of it by one individual does not actually or potentially reduce the amount available to be consumed by another individual." In a non-economic sense, the term is often used to describe something that is useful for the public generally, such as education and infrastructure, although these are not "public goods" in the economic sense. This is in contrast to a common good
which is non-excludable but is rivalrous to a certain degree.
Public goods include fresh
air, knowledge, official statistics, national security
, common language(s), flood
control systems, lighthouses, and street lighting. Public goods that are available everywhere are sometimes referred to as global public goods. There is an important conceptual difference between the sense of 'a' public good, or public 'goods' in economics, and the more generalized idea of 'the public good' (or common good, or public interest
),"‘the’ public good is a shorthand signal
for shared benefit at a societal level [this] (philosophical/political) sense should not be reduced to the established specific (economic) sense of ‘a’ public good."
Many public goods may at times be subject to excessive
use resulting in negative externalities
affecting all users; for example air pollution
and traffic congestion. Public goods problems are often closely related to the "free-rider" problem, in which people not paying for the good may continue to access it. Thus, the good may be under-produced, overused or degraded. Public goods may also become subject to restrictions on access and may then be considered to be club
goods or private goods; exclusion
mechanisms include copyright
, patents, congestion pricing
, and pay television.
There is a good deal of debate and literature on how to measure the significance of public goods problems in an economy, and to identify the best remedies.