a priori

[ ey prahy-awr-ahy, -ohr-ahy, ey pree-awr-ee, -ohr-ee, ah pree-awr-ee, -ohr-ee ]
/ ˌeɪ praɪˈɔr aɪ, -ˈoʊr aɪ, ˌeɪ priˈɔr i, -ˈoʊr i, ˌɑ priˈɔr i, -ˈoʊr i /
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See synonyms for: a priori / apriority on Thesaurus.com

from a general law to a particular instance; valid independently of observation.Compare a posteriori (def. 1).
existing in the mind prior to and independent of experience, as a faculty or character trait.Compare a posteriori (def. 2).
not based on prior study or examination; nonanalytic: an a priori judgment.


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Origin of a priori

1645–55; <Latin: literally, from the one before. See a-4, prior1


a·pri·or·i·ty [ey-prahy-awr-i-tee, -or-], /ˌeɪ praɪˈɔr ɪ ti, -ˈɒr-/, noun


ad hoc, a posteriori, a priori , ex post facto, prima facie
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023


What does a priori mean?

A priori is a term applied to knowledge considered to be true without being based on previous experience or observation. In this sense, a priori describes knowledge that requires no evidence.

A priori comes from Latin and literally translates as “from the previous” or “from the one before.”

It’s often applied to things involving deductive reasoning, which uses general principles to arrive at specific facts or conclusions (from cause to effect).

It can be used as an adjective, as in a priori knowledge, or as an adverb, as in We shouldn’t assume a priori that this is true.

A priori contrasts with a posteriori, which literally translates as “from the latter” or “from the one behind” and is applied to things that are based on experience, observation, or existing data. A posteriori is applied to things that involve inductive reasoning, which uses specific instances to arrive at a general principle or law (from effect to cause).

Both a priori and a posteriori are used in the context of reasoning and philosophy, especially epistemology, which is the philosophical study of knowledge. Both can also be used generally, though they’re often used formally.

Example: Any proposition considered to be a priori knowledge should be carefully examined for bias. ​

Where does a priori come from?

The first records of the use of a priori in English come from the mid-1600s. The first part, a, means “from,” and priori means “previous” (the English words prior and priority are based on the same root).

The terms a priori and a posteriori were popularized by philosopher Immanuel Kant in his influential 1781 book Critique of Pure Reason, which focuses on the distinction between empirical and non-empirical knowledge.

A priori knowledge is independent of experience, while a posteriori knowledge is derived from experience or observation. Things that are claimed to be true a priori are often thought to be self-evident, while those claimed to be true a posteriori are based on what has been experienced or demonstrated to be true.

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What are some other forms related to a priori?

  • apriority (noun)

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How is a priori used in real life?

A priori is primarily used in philosophy, but is also occasionally used in general conversation and writing.



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A priori knowledge is based on experience.

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British Dictionary definitions for a priori

a priori
/ (eɪ praɪˈɔːraɪ, ɑː prɪˈɔːrɪ) /

logic relating to or involving deductive reasoning from a general principle to the expected facts or effects
logic known to be true independently of or in advance of experience of the subject matter; requiring no evidence for its validation or support

Derived forms of a priori

apriority (ˌeɪpraɪˈɒrɪtɪ), noun

Word Origin for a priori

C18: from Latin, literally: from the previous (that is, from cause to effect)
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012