a posteriori

[ ey po-steer-ee-awr-ahy, -ohr-ahy, -awr-ee, -ohr-ee ]
/ ˌeɪ pɒˌstɪər iˈɔr aɪ, -ˈoʊr aɪ, -ˈɔr i, -ˈoʊr i /
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from particular instances to a general principle or law; based upon actual observation or upon experimental data: an a posteriori argument that derives the theory from the evidence.Compare a priori (def. 1).
not existing in the mind prior to or independent of experience.Compare a priori (def. 2).


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Origin of a posteriori

1615–25; <Latin: literally, from the one behind. See a-4, posterior


ad hoc, a posteriori , a priori, ex post facto, prima facie

Words nearby a posteriori

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022


What does a posteriori mean?

A posteriori is a term applied to knowledge considered to be true based on experience, observation, or existing data. In this sense, a posteriori describes knowledge that requires evidence.

A posteriori comes from Latin and literally translates as “from the latter” or “from the one behind.”

It’s often applied to things involving inductive reasoning, which uses specific instances to arrive at a general principle or law (from effect to cause).

It can be used as an adjective, as in a posteriori knowledge, or as an adverb, as in We acquire knowledge a posteriori—through experience.

A posteriori contrasts with a priori, which literally translates as “from the previous” or “from the one before” and is applied to things considered to be true without being based on previous experience or observation. A priori is applied to things that involve deductive reasoning, which uses general principles to arrive at specific facts or conclusions (from cause to effect).

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: It’s a scientist’s job to gather facts a posteriori by careful observation.

Where does a posteriori come from?

The first records of the use of a posteriori in English come from around 1620. The first part, a, means “from,” and posteriori means “behind” (the English word posterior is 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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How is a posteriori used in real life?

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



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A posteriori knowledge is thought to be self-evident.

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British Dictionary definitions for a posteriori

a posteriori
/ (eɪ pɒsˌtɛrɪˈɔːraɪ, -rɪ, ɑː) /

adjective logic
relating to or involving inductive reasoning from particular facts or effects to a general principle
derived from or requiring evidence for its validation or support; empirical; open to revision
statistics See posterior probability

Word Origin for a posteriori

C18: from Latin, literally: from the latter (that is, from effect to cause)
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