The word 'criterion' entered English in the early seventeenth century directly from Greek 'kritḗrion,' meaning 'a means of judging' or 'a standard for judgment.' The Greek word was formed from 'kritḗs' (judge), itself from the verb 'krínein' (to separate, to decide, to judge). The ultimate origin is the PIE root *krey-, meaning 'to sift, to separate, to distinguish' — a root whose descendants pervade the vocabulary of judgment, decision, and evaluation across the Indo-European languages.
The PIE root *krey- produced an extraordinary cluster of related English words, all connected through the concept of separation and discrimination. In the Greek branch: 'criterion' (standard of judgment), 'crisis' (Greek 'krísis,' originally the decisive moment in a disease when the patient either recovers or dies — a point of separation), 'critic' (from 'kritikós,' one skilled in judgment), 'critique,' 'critical,' and 'hypocrite' (from 'hypokritḗs,' literally 'one who judges beneath,' originally an actor who speaks from behind a mask, hence someone who pretends). In the Latin branch, 'krínein' has a cognate in 'cernere' (to sift, to separate, to decide), which produced 'discern' (to separate out, to perceive), 'concern' (to sift together), 'decree' (a decision), 'secret' (set apart), and 'certain' (decided, settled
In the Germanic branch, the root *krey- appears in Old English 'hriddel' or 'hridder' (a sieve — literally an instrument for separating), which survives in dialect English as 'riddle' in the sense of a coarse sieve used for sifting soil or gravel. This is a different word from 'riddle' meaning 'a puzzle,' which comes from a different root entirely.
The plural of 'criterion' has been a source of persistent grammatical anxiety in English. The Greek plural is 'kritḗria,' giving English 'criteria.' Purists insist that 'criteria' is plural only and that 'criterion' must be used for the singular. In practice, 'criteria' has been used as a singular noun since at least the nineteenth century ('this criteria is important'), though this usage is still condemned by most style guides. The pattern mirrors the history of 'data
The word gained particular prominence in philosophy and science. In philosophy, the 'criterion problem' — how we determine the standard by which truth claims are evaluated — goes back to the ancient skeptics. Sextus Empiricus devoted extensive argument to the question of whether any criterion of truth could be established without circular reasoning. In modern philosophy, Ludwig Wittgenstein's concept of criteria for the application of concepts
In science, 'criterion' and 'criteria' are used with technical precision. Statistical criteria (like the Akaike information criterion) provide mathematical standards for model selection. Medical diagnostic criteria define the conditions that must be met for a diagnosis. The Rayleigh criterion in optics specifies the minimum angular separation at which two point sources can be resolved.
The word 'Criterion' also became a famous proper noun: the Criterion Theatre in London's Piccadilly Circus, opened in 1874, and the Criterion Collection, the American home video company known for publishing art films, founded in 1984. Both names invoke the word's core meaning — a standard of quality or judgment.
From a PIE root meaning simply 'to sift grain from chaff,' the concept of separation evolved into the vocabulary of judgment, decision, and discernment that structures Western intellectual life. Every time we apply criteria, face a crisis, consult a critic, or identify a crime, we are using the linguistic descendants of the same ancient act of sorting.