All else being equal

Ceteris paribus or caeteris paribus is a Latin phrase meaning "other things equal". English translations of the phrase include "all other things being equal" or "other things held constant" or "all else unchanged". A prediction or a statement about a causal, empirical, or logical relation between two states of affairs is ceteris paribus if it is acknowledged that the prediction, although usually accurate in expected conditions, can fail or the relation can be abolished by intervening factors.

A ceteris paribus assumption is often key to scientific inquiry, as scientists seek to screen out factors that perturb a relation of interest. Thus, epidemiologists for example may seek to control independent variables as factors that may influence dependent variables—the outcomes or effects of interest. Likewise, in scientific modeling, simplifying assumptions permit illustration or elucidation of concepts thought relevant within the sphere of inquiry.

There is ongoing debate in the philosophy of science concerning ceteris paribus statements. On the logical empiricist view, fundamental physics tends to state universal laws, whereas other sciences, such as biology, psychology, and economics, tend to state laws that hold true in normal conditions but have exceptions, ceteris paribus laws (cp laws). The focus on universal laws is a criterion distinguishing fundamental physics as fundamental science, whereas cp laws are predominant in most other sciences as special sciences, whose laws hold in special cases. This distinction assumes a logical empiricist view of science. It does not readily apply in a mechanistic understanding of scientific discovery. There is reasonable disagreement as to whether mechanisms or laws are the appropriate model, though mechanisms are the favored method.

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