# priori

/pɹaɪˈɔˌɹaɪ/ (US) · CEFR C1 · Adjective

Source: https://englishreference.com/word/priori
Updated: 2026-05-26

## Definition

based on what you already know or believe, rather than on facts you have seen. It is often used in science or math to describe a belief before testing it.

For teachers: based on what is known or assumed before experience or observation. Often used in the phrase 'a priori' to describe reasoning that proceeds from general principles to specific instances.

## Examples

- The scientist had an a priori belief that the experiment would fail.
- The researchers started with an a priori assumption that the new drug would be effective, but they needed data to confirm it.
- In formal logic, an a priori argument is one that is considered valid regardless of empirical evidence, relying solely on the structure of the premises themselves.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.