Ceteris Paribus: Holding Other Things Equal

What the Latin phrase ceteris paribus means, why economists use it to isolate cause and effect, and how it can be misunderstood.

Economists often use the Latin phrase ceteris paribus, meaning “other things being equal” or “all else held constant”. It is one of the most important ideas for understanding economic reasoning.

Why it is needed

The real economy has countless things changing at once. Prices, incomes, weather, technology, government policy and tastes all shift at the same time. To understand how one factor affects another, economists imagine changing just one thing while keeping everything else the same.

For example, the law of demand says that when the price of a good rises, people buy less of it, ceteris paribus. That means: if nothing else changes, such as incomes, the prices of other goods or people’s preferences.

An example

Suppose the price of mangoes rises, yet people buy more mangoes. Does this disprove the law of demand? Not necessarily. Perhaps incomes also rose, or a festival increased demand. The law of demand describes the effect of price alone, holding other factors constant. In the real world, the other factors also changed.

Ceteris paribus in models

Economic models use ceteris paribus to make complex questions manageable. By focusing on a few variables, models can show clear cause-and-effect relationships. Later, economists can relax the assumption and consider how several factors interact.

Studying the effect of rain on crops

A researcher wants to know how rainfall affects rice yields. But yields also depend on fertiliser, seeds and temperature. By comparing fields that are similar in everything except rainfall, the researcher can estimate the effect of rain, ceteris paribus. Without this approach, the effect of rain would be mixed up with everything else.

Limitations

In reality, other things rarely stay equal. Policies can have ripple effects that change many variables at once. A tax cut, for example, might change prices, incomes and interest rates simultaneously. Good economic analysis uses ceteris paribus as a starting point, then considers how other factors respond.

Thinking a real-world exception disproves an economic law

When prices and quantities move together in an unexpected way, it usually means other factors changed too. Economic principles describe the effect of one change with other things held constant, not every real-world outcome.

Key takeaways

Ceteris paribus means other things being equal.
It lets economists isolate the effect of one factor.
Real-world data often mixes several changes, so apparent exceptions may not disprove a principle.
Good analysis starts with ceteris paribus, then considers how other factors respond.