The analytical convention of holding all other variables constant while examining the effect of changing one. Latin for "all else equal," it isolates a single causal channel by freezing the rest of the system, making partial-equilibrium reasoning tractable at the cost of ignoring feedback and general-equilibrium spillovers.
How it works
An analyst fixes every variable except the one under study, then traces that variable's marginal effect on the outcome. It underpins comparative statics and partial-equilibrium analysis, but breaks down when the held-constant variables in fact co-move with the variable being shocked — the assumption becomes false precisely when second-round effects, expectations, or policy responses dominate.
Why it matters now
Much 2025-26 macro commentary rests on a false ceteris-paribus assumption — claiming a tariff, rate cut, or fiscal shock has a clean isolated effect while ignoring that FX, term premia, and inflation expectations all move simultaneously. The phrase is shorthand for flagging this fallacy.
Example
A claim that "a 100bp Fed cut lowers 10-year yields by 100bp" rests on a false ceteris-paribus assumption: in practice a cut can steepen the curve via higher inflation expectations and term premium, so long-end yields may rise — as seen after the September 2024 cut, when 10-year Treasury yields climbed roughly 60bp into year-end despite the easing.
Frequently asked
- What is the ceteris-paribus assumption?
- The ceteris-paribus assumption holds all other variables constant while isolating the effect of changing one. Latin for "all else equal," it lets analysts trace a single causal channel through comparative statics and partial-equilibrium reasoning. It makes problems tractable but ignores feedback, expectations, and general-equilibrium spillovers that often dominate real outcomes.
- Why does ceteris paribus matter for macro forecasting?
- Ceteris paribus matters because most macro shocks violate it: tariffs, rate cuts, and fiscal impulses move FX, term premia, and inflation expectations simultaneously. A forecast that isolates one channel while pretending the rest of the system is frozen will misjudge magnitude and sometimes sign. Flagging a false all-else-equal claim is a core analytical discipline on any macro desk.
- How does ceteris paribus differ from general equilibrium?
- Ceteris paribus is partial-equilibrium reasoning that freezes everything except one variable, while general equilibrium lets all variables adjust until the whole system clears. Partial analysis answers "what is the direct effect?"; general equilibrium answers "what is the net effect after every market and expectation re-prices?" The two diverge most when second-round effects are large.
- When does the ceteris-paribus assumption break down?
- The ceteris-paribus assumption breaks down whenever the held-constant variables actually co-move with the variable being shocked. This happens when expectations, policy reaction functions, or feedback loops dominate — precisely the conditions of a regime shift. The September 2024 Fed cut illustrates it: 10-year Treasury yields rose roughly 60bp into year-end despite easing, as inflation expectations and term premium
Glossary · term premium
The term premium is the extra yield investors demand to hold a long-dated bond instead of rolling short-dated instruments over the same horizon. It compensates for the risk that future short rates, inflation, or fiscal supply diverge from expectations, and is the residual in nominal yields once the expected-rates path is stripped out.
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- Is ceteris paribus a flaw or a useful tool?
- Ceteris paribus is both: a deliberate simplification that isolates causal channels, and a fallacy when applied to interconnected systems uncritically. The convention is indispensable for clean comparative statics, but on a desk it functions mostly as a warning label — invoked to flag when a clean isolated-effect claim quietly ignores the feedback that determines the real outcome.