English Reference
noun

assertion

n.
US /əˈsɝʃən/ UK /ɐsˈɜːʃən/ as·ser·tion UK spelling assertion's, assertion's

  1. 01 C1 Advanced AcademicFormal

    a statement where you say something is true, often with a lot of confidence.

    a confident and forceful statement of fact or belief, often made without immediate proof.

    Simple

    The lawyer made an assertion that his client was innocent of the crime.

    In context

    The author's central assertion is that economic stability depends more on psychological factors than on physical resources.

    Usage

    Often followed by a 'that' clause or the preposition 'of'.

    denialdisavowal
  2. 02 C1 Advanced Formal

    the act of making sure your rights or power are recognized.

    the act of asserting or insisting upon one's rights, authority, or influence.

    Simple

    The small country's assertion of its independence surprised the world.

    In context

    The sudden assertion of executive power by the board led to a series of resignations among the senior management team.

  3. 03 C2 Proficiency Technical Computing

    a command in a computer program that checks if a condition is true while the code is running.

    a boolean expression at a specific point in a program which will be true unless there is a bug in the code.

    Simple

    The programmer added an assertion to make sure the user's age was not a negative number.

    In context

    If the assertion fails during the execution of the test suite, the program will terminate immediately to prevent further data corruption.

    Usage

    Commonly used in the context of 'failed assertion' or 'assertion error'.

  4. 04 C2 Proficiency TechnicalFormal Law

    a claim made by a company about its money that an accountant checks.

    a representation or declaration made by management regarding the recognition, measurement, and presentation of items in financial statements.

    Simple

    The auditor checked the company's assertion that it owned all the equipment listed.

    In context

    The audit team must obtain sufficient evidence to support management's assertion regarding the valuation of intangible assets.

The assertion that sex is binary is essentially saying that people are what scientists call sexually dimorphic – that is, the sex-related biological traits of females and males don’t overlap.

The Conversation· 17 Aug 2026

Speaking to reporters on Friday, Trump rejected the assertion that the families of those on board the aircraft carrier are worried about their loved ones.

Al Jazeera· 14 Aug 2026

From Middle English assercioun, from Latin assertiō. By surface analysis, assert + -ion.

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

This entry
Origin Latin assertiō
Level C1 · Advanced
Frequency Frequent
Updated