An ordinary good is a microeconomic

Microeconomics

Microeconomics is a branch of economics that studies the behavior of how the individual modern household and firms make decisions to allocate limited resources. Typically, it applies to markets where goods or services are being bought and sold...

 concept used in consumer theory

Consumer theory

Consumer choice is a theory of microeconomics that relates preferences for consumption goods and services to consumption expenditures and ultimately to consumer demand curves. The link between personal preferences, consumption, and the demand curve is one of the most closely studied relations in...

. It is defined as a good

Good (economics and accounting)

In economics, a good is something that is intended to satisfy some wants or needs of a consumer and thus has economic utility. It is normally used in the plural form—goods—to denote tangible commodities such as products and materials....

 which creates increased demand when the price for the good drops or conversely decreased demand if the price for the good increases, ceteris paribus

Ceteris paribus

or is a Latin phrase, literally translated as "with other things the same," or "all other things being equal or held constant." It is an example of an ablative absolute and is commonly rendered in English as "all other things being equal." A prediction, or a statement about causal or logical...

. It is the opposite of a Giffen good

Giffen good

In economics and consumer theory, a Giffen good is one which people paradoxically consume more of as the price rises, violating the law of demand. In normal situations, as the price of a good rises, the substitution effect causes consumers to purchase less of it and more of substitute goods...

.

Since the existence of Giffen goods outside the realm of economic theory is still contested, the pairing of Giffen goods with ordinary goods has gotten less traction in economics textbooks than the pairing normal good

Normal good

In economics, normal goods are any goods for which demand increases when income increases and falls when income decreases but price remains constant, i.e. with a positive income elasticity of demand...

/inferior good

Inferior good

In consumer theory, an inferior good is a good that decreases in demand when consumer income rises, unlike normal goods, for which the opposite is observed. Normal goods are those for which consumers' demand increases when their income increases....

 used to distinguish responses to income changes. The usage of "ordinary good" is still useful since it allows a simple representation of price and income changes. A normal good is always ordinary, while an ordinary good can be either normal or inferior.

Distinction between income and price effects

Income change				Price change
	Normal good Normal good In economics, normal goods are any goods for which demand increases when income increases and falls when income decreases but price remains constant, i.e. with a positive income elasticity of demand...	Inferior good Inferior good In consumer theory, an inferior good is a good that decreases in demand when consumer income rises, unlike normal goods, for which the opposite is observed. Normal goods are those for which consumers' demand increases when their income increases....			Ordinary good	Giffen good Giffen good In economics and consumer theory, a Giffen good is one which people paradoxically consume more of as the price rises, violating the law of demand. In normal situations, as the price of a good rises, the substitution effect causes consumers to purchase less of it and more of substitute goods...
Income up	Consumption up	Consumption down		Price up	Consumption down	Consumption up
Income down	Consumption down	Consumption up		Price down	Consumption up	Consumption down

See also

• Supply and demand
  Supply and demand
  Supply and demand is an economic model of price determination in a market. It concludes that in a competitive market, the unit price for a particular good will vary until it settles at a point where the quantity demanded by consumers will equal the quantity supplied by producers , resulting in an...
  
  
• Consumer theory
  Consumer theory
  Consumer choice is a theory of microeconomics that relates preferences for consumption goods and services to consumption expenditures and ultimately to consumer demand curves. The link between personal preferences, consumption, and the demand curve is one of the most closely studied relations in...
  
  
• Giffen good
  Giffen good
  In economics and consumer theory, a Giffen good is one which people paradoxically consume more of as the price rises, violating the law of demand. In normal situations, as the price of a good rises, the substitution effect causes consumers to purchase less of it and more of substitute goods...
  
  
• Inferior good
  Inferior good
  In consumer theory, an inferior good is a good that decreases in demand when consumer income rises, unlike normal goods, for which the opposite is observed. Normal goods are those for which consumers' demand increases when their income increases....
  
  
• Normal good
  Normal good
  In economics, normal goods are any goods for which demand increases when income increases and falls when income decreases but price remains constant, i.e. with a positive income elasticity of demand...
  
  
• Capital good
  Capital good
  A capital good, or simply capital in economics, is a manufactured means of production. Capital goods are acquired by a society by saving wealth which can be invested in the means of production....