ab initio


ab in·​i·​tio ˌab-ə-ˈni-shē-ˌō How to pronounce ab initio (audio)
: from the beginning

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Starting Things With Ab Initio

We'll tell you right from the beginning where ab initio comes from. This adverb was adopted at the beginning of the 17th century directly from Latin, where it translates as "from the beginning." (Initio is a form of the noun initium, meaning "beginning," which gave rise to such English words as initial, initiate, and initiative.) Ab initio most frequently appears in legal contexts, but it is not surprising to find it used outside of the courtroom. The phrase is also used as an adjective meaning "starting from or based on first principles" (as in "predicted from ab initio calculations").

Examples of ab initio in a Sentence

Recent Examples on the Web Even less so is the 1917 Liberty Bond Act, which has long since been superseded by a new Congressional budget process that has determined its own ‘ceiling’ by budgeting itself since 1974, and was of doubtful 14th Amendment conformity, at least as now interpreted by Republicans, ab initio in 1917. Robert Hockett, Forbes, 7 May 2023 So, the ability to scale and diversify must be built ab initio into any decision to build a syn-bio stack. Nicolas Goeldel, Fortune, 3 Mar. 2023 But some countries do not allow either of these procedures, and instead require that the whole lawsuit be tried ab initio as if the foreign proceedings never occurred. Jay Adkisson, Forbes, 23 Jan. 2023 What McConnell needed to do, for his argument to establish its conclusions, was to provide independent grounds of some kind for ruling out Interpretation B ab initio. Jason Lee Steorts, National Review, 15 May 2021 Moreover, the Executive Order exceeds the President’s authority and is therefore ultra vires and void ab initio. Eriq Gardner, Billboard, 4 Sep. 2020

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'ab initio.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


Latin ab initiō

First Known Use

1600, in the meaning defined above

Time Traveler
The first known use of ab initio was in 1600


Dictionary Entries Near ab initio

Cite this Entry

“Ab initio.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/ab%20initio. Accessed 30 Sep. 2023.

Legal Definition

ab initio

: from the beginning
a contract found to be void ab initio


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