Time | Definition & Facts

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border-right-sm border-left-sm open"> <div class="drawer d-flex flex-column open"> <div class="left-rail-section-content"> <div class="topic-left-rail-header text-truncate bg-gray-50 position-relative text-right d-flex align-items-center"> <div class="tlr-title px-20 py-15 text-left"> <em class="material-icons text-gray-400 d-lg-none" data-icon="toc"></em> <a class="font-serif font-weight-bold text-black link-blue" href="https://www.britannica.com/science/time">time</a> </div> <button aria-label="Close" class="js-sections-close-button btn-link btn-sm btn d-lg-none position-absolute top-0 p-10 right-0" > <em class="material-icons font-26" data-icon="close"></em> </button> </div> <div class="section-content pl-10 pr-20 pl-sm-50 pr-sm-60 pl-lg-5 pr-lg-10 pt-10 pt-lg-0 bg-gray-50 clear-catfish-ad"> <div class="toc mb-20"> <div class="font-serif font-14 font-weight-bold mx-15 mb-15 mt-20"> Table of Contents </div> <ul class="list-unstyled my-0" data-level="h1"><li data-target="#ref1"><div class="pl-25"><a class="link-gray-900 w-100" href="/science/time">Introduction</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref61000"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/science/time#ref61000">Time and its role in the history of thought and action</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref61001"><a class="w-100 link-gray-900" href="/science/time#ref61001">Nature and definition of time</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref61002"><a class="w-100 link-gray-900" href="/science/time/Prescientific-conceptions-of-time-and-their-influence">Prescientific conceptions of time and their influence</a><ul class="list-unstyled" data-level="h3"><li data-target="#ref61003"><a class="w-100 link-gray-900" href="/science/time/Prescientific-conceptions-of-time-and-their-influence#ref61003">The individual’s experience and observation of time</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref61004" class="has-children"><a class="w-100 link-gray-900" href="/science/time/Cyclic-view-of-time-in-the-philosophy-of-history">Cyclic view of time in the philosophy of history</a><ul class="list-unstyled" data-level="h4"><li data-target="#ref61005"><a class="w-100 link-gray-900" href="/science/time/Cyclic-view-of-time-in-the-philosophy-of-history#ref61005">Environmental recurrences and religion</a></li></ul><ul class="list-unstyled" data-level="h4"><li data-target="#ref61006"><a class="w-100 link-gray-900" href="/science/time/Cyclic-view-of-time-in-the-philosophy-of-history#ref61006">The cyclic view in various cultures</a></li></ul></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref61007"><a class="w-100 link-gray-900" href="/science/time/One-way-view-of-time-in-the-philosophy-of-history">One-way view of time in the philosophy of history</a></li></ul></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref61008"><a class="w-100 link-gray-900" href="/science/time/One-way-view-of-time-in-the-philosophy-of-history#ref61008">Early modern and 19th-century scientific philosophies of time</a></li></ul></div></li><li data-target="#ref61009"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/science/time/Contemporary-philosophies-of-time">Contemporary philosophies of time</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref61010"><a class="w-100 link-gray-900" href="/science/time/Contemporary-philosophies-of-time#ref61010">Time in 20th-century philosophy of physics</a><ul class="list-unstyled" data-level="h3"><li data-target="#ref61011"><a class="w-100 link-gray-900" href="/science/time/Contemporary-philosophies-of-time#ref61011">Time in the special theory of relativity</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref61012"><a class="w-100 link-gray-900" href="/science/time/Time-in-general-relativity-and-cosmology">Time in general relativity and cosmology</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref61013" class="has-children"><a class="w-100 link-gray-900" href="/science/time/Time-in-microphysics">Time in microphysics</a><ul class="list-unstyled" data-level="h4"><li data-target="#ref61014"><a class="w-100 link-gray-900" href="/science/time/Time-in-microphysics#ref61014">Quantum mechanical aspects of time</a></li></ul><ul class="list-unstyled" data-level="h4"><li data-target="#ref61015"><a class="w-100 link-gray-900" href="/science/time/Time-in-microphysics#ref61015">Time in particle interactions</a></li></ul></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref61016"><a class="w-100 link-gray-900" href="/science/time/Time-in-microphysics#ref61016">Time in molar physics</a></li></ul></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref61017"><a class="w-100 link-gray-900" href="/science/time/Time-in-20th-century-philosophy-of-biology-and-philosophy-of-mind">Time in 20th-century philosophy of biology and philosophy of mind</a></li></ul></div></li><li data-target="#ref61018"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/science/time/Time-as-systematized-in-modern-scientific-society">Time as systematized in modern scientific society</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref61019"><a class="w-100 link-gray-900" href="/science/time/Time-as-systematized-in-modern-scientific-society#ref61019">Time measurement: general concepts</a><ul class="list-unstyled" data-level="h3"><li data-target="#ref61020"><a class="w-100 link-gray-900" href="/science/time/Time-as-systematized-in-modern-scientific-society#ref61020">Principal scales</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref61021"><a class="w-100 link-gray-900" href="/science/time/Time-as-systematized-in-modern-scientific-society#ref61021">Relativistic effects</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref61022"><a class="w-100 link-gray-900" href="/science/time/Time-as-systematized-in-modern-scientific-society#ref61022">Clocks</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref61023" class="has-children"><a class="w-100 link-gray-900" href="/science/time/Time-as-systematized-in-modern-scientific-society#ref61023">Time units and calendar divisions</a><ul class="list-unstyled" data-level="h4"><li data-target="#ref61024"><a class="w-100 link-gray-900" href="/science/time/Lengths-of-years-and-months">Lengths of years and months</a></li></ul><ul class="list-unstyled" data-level="h4"><li data-target="#ref61025"><a class="w-100 link-gray-900" href="/science/time/Lengths-of-years-and-months#ref61025">Astronomical years and dates</a></li></ul></li></ul></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref61026"><a class="w-100 link-gray-900" href="/science/time/Lengths-of-years-and-months#ref61026">Rotational time</a><ul class="list-unstyled" data-level="h3"><li data-target="#ref61027"><a class="w-100 link-gray-900" href="/science/time/Standard-time">Standard time</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref61028"><a class="w-100 link-gray-900" href="/science/time/Standard-time#ref61028">Universal Time</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref61029"><a class="w-100 link-gray-900" href="/science/time/Standard-time#ref61029">Variations in the Earth’s rotation rate</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref61030"><a class="w-100 link-gray-900" href="/science/time/Standard-time#ref61030">Coordinated Universal Time; leap seconds</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref61031"><a class="w-100 link-gray-900" href="/science/time/Time-determination">Time determination</a></li></ul></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref61032"><a class="w-100 link-gray-900" href="/science/time/Time-determination#ref61032">Dynamical time</a><ul class="list-unstyled" data-level="h3"><li data-target="#ref61033"><a class="w-100 link-gray-900" href="/science/time/Time-determination#ref61033">Ephemeris Time</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref61034"><a class="w-100 link-gray-900" href="/science/time/Time-determination#ref61034">Ephemeris second</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref61035"><a class="w-100 link-gray-900" href="/science/time/Time-determination#ref61035">TDB and TDT</a></li></ul></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref61036"><a class="w-100 link-gray-900" href="/science/time/Atomic-time">Atomic time</a><ul class="list-unstyled" data-level="h3"><li data-target="#ref61037"><a class="w-100 link-gray-900" href="/science/time/Atomic-time#ref61037">Basic principles</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref61038" class="has-children"><a class="w-100 link-gray-900" href="/science/time/Atomic-time#ref61038">Atomic clocks</a><ul class="list-unstyled" data-level="h4"><li data-target="#ref61039"><a class="w-100 link-gray-900" href="/science/time/Atomic-time#ref61039">Cesium clocks</a></li></ul><ul class="list-unstyled" data-level="h4"><li data-target="#ref61040"><a class="w-100 link-gray-900" href="/science/time/Atomic-time#ref61040">Other atomic clocks</a></li></ul></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref61041"><a class="w-100 link-gray-900" href="/science/time/Atomic-time#ref61041">SI second</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref61042"><a class="w-100 link-gray-900" href="/science/time/Atomic-time-scales">Atomic time scales</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref61043"><a class="w-100 link-gray-900" href="/science/time/Atomic-time-scales#ref61043">Time and frequency dissemination</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref61044"><a class="w-100 link-gray-900" href="/science/time/Atomic-time-scales#ref61044">Relativistic effects</a></li></ul></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref61045"><a class="w-100 link-gray-900" href="/science/time/Atomic-time-scales#ref61045">Pulsar time</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref61046"><a class="w-100 link-gray-900" href="/science/time/Radiometric-time">Radiometric time</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref61047"><a class="w-100 link-gray-900" href="/science/time/Radiometric-time#ref61047">Problems of cosmology and uniform time</a></li></ul></div></li></ul> <a class="toc-extra-link link-gray-900" href="https://www.britannica.com/science/time/additional-info">References & Edit History</a> <a class="toc-extra-link link-gray-900" href="/facts/time">Related Topics</a> </div> 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Emeritus Professor of Philosophy, University of Adelaide, Australia. Author of <em>Philosophy...</em></div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline"> John Jamieson Carswell Smart</span>, <div class="editor-popover popover p-0"> <a class="d-block p-20 qa-editor-popup gtm-byline font-12 byline-contributor" href="/contributor/William-Markowitz/1905" > <div class="editor-title font-16 font-weight-bold">William Markowitz</div> <div class="editor-description font-12 font-serif mt-5 clamp-description text-black"> Adjunct Professor of Physics, Nova University, Fort Lauderdale, Fla., 1972–91. Astronomer, U.S. Naval Observatory, Washington, D.C., 1936–66; Director, Time Service, 1953–66. Coeditor of <i>Continental...</i></div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline"> William Markowitz</span><span class="text-gray-700 mx-5">•</span><a class="see-all border-gray-700 gtm-byline" rel="nofollow" href="https://www.britannica.com/science/time/additional-info#contributors">All</a> </div> <div class="font-serif font-12 text-gray-700"> <span class="qa-fact-checked-by">Fact-checked by</span> <div class="editor-popover popover p-0"> <a class="d-block p-20 qa-editor-popup font-12" href="/editor/The-Editors-of-Encyclopaedia-Britannica/4419" > <div class="editor-title font-16 font-weight-bold">The Editors of Encyclopaedia Britannica</div> <div class="editor-description font-12 font-serif mt-5 text-black">Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link font-12 "> The Editors of Encyclopaedia Britannica</span></div> <div class="last-updated font-12 font-serif"> <span class="text-gray-700"> Last Updated: <time datetime="2025-02-12T00:00:00CST" >Feb 12, 2025</time> •</span> <a class="byline-edit-history" href="https://www.britannica.com/science/time/additional-info#history" rel="nofollow">Article History</a> </div></div> </div> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button d-none d-sm-block js-sections-inline-button module-spacing btn d-lg-none"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <div class="d-flex d-sm-none flex-row"> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button js-sections-inline-button module-spacing"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <button class="ai-ask-button btn border-2 ai-ask-button btn border-2 module-spacing btn-sm js-inline-ai-ask-button btn-outline-red-400 border-red-400 p-10 ml-5"> Ask the Chatbot a Question </button> </div> <div class="js-qf-module qf-module px-40 px-sm-20 py-15 mx-auto module-spacing font-14 bg-gray-50 rounded"> <div class="facts-list mt-10"> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>Key People: </dt> <dd><a href="/biography/Henri-Bergson" topicid="61856">Henri Bergson</a></dd> <dd><a href="/biography/Ferdinand-Berthoud" topicid="62820">Ferdinand Berthoud</a></dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> </div> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>Related Topics: </dt> <dd><a href="/science/time-perception" topicid="596177">time perception</a></dd> <dd><a href="/science/dynamical-time" topicid="175179">dynamical time</a></dd> <dd><a href="/science/time-dilation" topicid="596118">time dilation</a></dd> <dd><a href="/science/solar-time" topicid="553052">solar time</a></dd> <dd><a href="/science/twin-paradox" topicid="121978">twin paradox</a></dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> <div class="text-center"> <a class="btn btn-sm btn-link p-0" href="/facts/time"> See all related content </a> </div> </div> </div> </div><div class="bg-gray-50 p-15 rounded module-spacing recent-news d-flex flex-column float-false"> <div> <h2 class="font-weight-bold font-14 m-0 d-inline"> News <span class="text-gray-600">•</span> </h2> <div class="recent-news-item first-recent-news-item d-inline"> <a class="font-14 gtm-ap-news-link" href="/news/596034/ba95fc9ec297102cc05097ac3ad008a6" rel="nofollow">Super Bowl 2025: Time, channel, halftime show, how to watch Chiefs vs. Eagles livestream</a> <span class="font-14 text-gray-600"> <span>•</span> Feb. 12, 2025, 8:32 PM ET (AP) </span> </div> </div> <div class="rest-of-recent-news-items"> <button class="js-toggle-recent-news d-flex btn btn-unstyled font-14 pr-10 rounded-sm mt-10" aria-label="Toggle additional news items"> Show less <em class="material-icons" data-icon="expand_less"></em> </button> </div> </div><span class="marker before-article"></span><section data-level="1" id="ref1"><span class="marker PREMOD1 mod-inline"></span><p class="topic-paragraph"><strong><span id="ref368277"></span>time</strong>, a measured or measurable period, a <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="continuum" href="https://www.merriam-webster.com/dictionary/continuum" data-type="MW">continuum</a> that lacks spatial dimensions. Time is of philosophical interest and is also the subject of mathematical and scientific investigation.</p><span class="marker MOD1 mod-inline"></span></section> <span class="marker h2"></span><section data-level="1" id="ref61000"> <h2 class="h1">Time and its role in the history of thought and action</h2> <section data-level="2" id="ref61001"> <h2 class="h2"><span id="ref368278"></span><a href="https://www.britannica.com/topic/metaphysics" class="md-crosslink " data-show-preview="true">Nature and definition of time</a></h2> <span class="marker PREMOD2 mod-inline"></span><p class="topic-paragraph">Time appears to be more puzzling than <a href="https://www.britannica.com/science/space-physics-and-metaphysics" class="md-crosslink autoxref " data-show-preview="true">space</a> because it seems to flow or pass or else people seem to advance through it. But the passage or advance seems to be unintelligible. The question of how many seconds per second time flows (or one advances through it) is obviously an absurd one, for it suggests that the flow or advance <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="comprises" href="https://www.merriam-webster.com/dictionary/comprises" data-type="MW">comprises</a> a rate of change with respect to something else—to a sort of hypertime. But if this hypertime itself flows, then a hyper-hypertime is required, and so on, ad infinitum. Again, if the world is <a href="https://www.britannica.com/topic/thought" class="md-crosslink autoxref " data-show-preview="true">thought</a> of as spread out in <a href="https://www.britannica.com/science/space-time" class="md-crosslink " data-show-preview="true">space-time</a>, it might be asked whether human <a href="https://www.britannica.com/topic/consciousness" class="md-crosslink autoxref " data-show-preview="true">consciousness</a> advances up a timelike direction of this world and, if so, how fast; whether future events pop into <a href="https://www.britannica.com/topic/existence" class="md-crosslink autoxref " data-show-preview="true">existence</a> as the “now” reaches them or are there all along; and how such changes in space-time can be represented, since time is already within the picture. (Ordinary change can, of course, be represented in a space-time picture: for example, a particle at rest is represented by a straight line and an oscillating particle by a wavy line.)</p><span class="marker MOD2 mod-inline"></span> <span class="marker PREMOD3 mod-inline"></span><p class="topic-paragraph">In the face of these difficulties, philosophers tend to divide into two sorts: the “<span id="ref368279"></span><a href="https://www.britannica.com/topic/process-philosophy" class="md-crosslink " data-show-preview="true">process philosophers</a>” and the “philosophers of the manifold.” Process philosophers—such as <span id="ref368280"></span><a href="https://www.britannica.com/biography/Alfred-North-Whitehead" class="md-crosslink " data-show-preview="true">Alfred North Whitehead</a>, an Anglo-American mathematician, scientist. and metaphysician who died in 1947—hold that the flow of time (or human advance through it) is an important <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="metaphysical" href="https://www.merriam-webster.com/dictionary/metaphysical" data-type="MW">metaphysical</a> fact. Like the French intuitionist <span id="ref368281"></span><a href="https://www.britannica.com/biography/Henri-Bergson" class="md-crosslink " data-show-preview="true">Henri Bergson</a>, they may hold that this flow can be grasped only by nonrational <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="intuition" href="https://www.merriam-webster.com/dictionary/intuition" data-type="MW">intuition</a>. Bergson even held that the scientific concept of time as a <a href="https://www.britannica.com/science/dimension-geometry" class="md-crosslink autoxref " data-show-preview="true">dimension</a> actually misrepresents reality. Philosophers of the manifold hold that the flow of time or human advance through time is an <a href="https://www.britannica.com/topic/illusion" class="md-crosslink autoxref " data-show-preview="true">illusion</a>. They argue, for example, that words such as <em><span id="ref368282"></span><a href="https://www.britannica.com/science/past" class="md-crosslink ">past</a></em>, <em><span id="ref368283"></span><a href="https://www.britannica.com/science/future" class="md-crosslink ">future</a></em>, and<em><span id="ref368284"></span><a href="https://www.britannica.com/science/present" class="md-crosslink "> now</a></em>, as well as the tenses of verbs, are indexical expressions that refer to the act of their own utterance. Hence, the <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="alleged" href="https://www.merriam-webster.com/dictionary/alleged" data-type="MW">alleged</a> change of an event from being future to being past is an <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="illusion" href="https://www.merriam-webster.com/dictionary/illusion" data-type="MW">illusion</a>. To say that the event is future is to assert that it is later than this utterance. Then later yet, when one says that it is in the past, he or she asserts that it is earlier than that other utterance. <em>Past</em> and <em>future</em> are not real <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="predicates" href="https://www.merriam-webster.com/dictionary/predicates" data-type="MW">predicates</a> of events in this view; and change in respect of them is not a genuine change.</p><span class="marker MOD3 mod-inline"></span> <span class="marker PREMOD4 mod-inline"></span><p class="topic-paragraph">Again, although process philosophers think of the future as somehow open or indeterminate, whereas the past is unchangeable, fixed, determinate, philosophers of the manifold hold that it is as much nonsense to talk of changing the future as it is to talk of changing the past. If a person decides to point left rather than to point right, then pointing left <em>is</em> what the future was. Moreover, this thesis of the determinateness of the future, they argue, must not be confused with <span id="ref368285"></span><a href="https://www.britannica.com/topic/determinism" class="md-crosslink " data-show-preview="true">determinism</a>, the theory that there are laws whereby later states of the <a href="https://www.britannica.com/science/universe" class="md-crosslink autoxref " data-show-preview="true">universe</a> may be <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="deduced" href="https://www.britannica.com/dictionary/deduced" data-type="EB">deduced</a> from earlier states (or vice versa). The <a href="https://www.britannica.com/topic/philosophy" class="md-crosslink autoxref " data-show-preview="true">philosophy</a> of the manifold is neutral about this issue. Future events may well exist and yet not be connected in a sufficiently lawlike way with earlier ones.</p><span class="marker MOD4 mod-inline"></span> <span class="marker PREMOD5 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="70933" data-asm-type="image"><div class="md-assembly-wrapper card-media" data-type="image"><a href="https://cdn.britannica.com/94/58594-050-1C569301/St-Augustine-Sandro-Botticelli-Ognissanti-church-Florence.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/596034/70933"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/94/58594-050-1C569301/St-Augustine-Sandro-Botticelli-Ognissanti-church-Florence.jpg?w=300"><img src="https://cdn.britannica.com/94/58594-050-1C569301/St-Augustine-Sandro-Botticelli-Ognissanti-church-Florence.jpg?w=300" alt="St. Augustine" data-width="1189" data-height="1600" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/94/58594-050-1C569301/St-Augustine-Sandro-Botticelli-Ognissanti-church-Florence.jpg" data-href="/media/1/596034/70933">St. Augustine</a><span>St. Augustine, fresco by Sandro Botticelli, 1480; in the Church of Ognissanti, Florence.</span><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">One of the features of time that puzzled the Neoplatonist philosopher <a href="https://www.britannica.com/biography/Saint-Augustine" class="md-crosslink " data-show-preview="true">Augustine of Hippo</a>, in the 5th century <span class="text-smallcaps">ce</span>, was the difficulty of defining it. In one <a href="https://www.britannica.com/science/electric-current" class="md-crosslink autoxref " data-show-preview="true">current</a> of 20th-century <span id="ref368286"></span><a href="https://www.britannica.com/topic/philosophy-of-language" class="md-crosslink " data-show-preview="true">philosophy of language</a>, however (that influenced by <a href="https://www.britannica.com/biography/Ludwig-Wittgenstein" class="md-crosslink " data-show-preview="true">Ludwig Wittgenstein</a>), no mystery was seen in this task. Learning to handle the word <em>time</em> involves a multiplicity of verbal skills, including the ability to handle such connected words as <em>earlier</em>, <em>later</em>, <em>now</em>, <em>second</em>, and <em>hour</em>. These verbal skills have to be picked up in very complex ways (partly by ostension), and it is not surprising that the meaning of the word <em>time</em> cannot be <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="distilled" href="https://www.britannica.com/dictionary/distilled" data-type="EB">distilled</a> into a neat verbal definition. (It is not, for example, an abbreviating word like <em>bachelor</em>.)</p><a class="link-module shadow-sm d-block qa-quiz-module" href="/quiz/all-about-physics-quiz" data-link-module-iframe-link=""> <img loading="lazy" src="https://cdn.britannica.com/03/221503-131-D7173869/Italian-physicist-Guglielmo-Marconi-at-work-on-his-yacht-Electra.jpg" alt="Italian physicist Guglielmo Marconi at work in the wireless room of his yacht Electra, c. 1920." class="rounded-sm mr-15" width="70" /> <div class="line-clamp clamp-5"> <div class="module-title bg-green">Britannica Quiz</div> <div class="font-weight-semi-bold mt-5">All About Physics Quiz</div> </div> </a><div class="one-good-fact-module"> </div><span class="marker MOD5 mod-inline"></span> <span class="marker PREMOD6 mod-inline"></span><p class="topic-paragraph">The philosophy of time bears powerfully on human emotions. Not only do individuals regret the past, they also fear the future, not least because the alleged flow of time seems to be sweeping them toward their <span id="ref368287"></span><a href="https://www.britannica.com/science/death" class="md-crosslink " data-show-preview="true">deaths</a>, as swimmers are swept toward a waterfall.</p><span class="marker MOD6 mod-inline"></span> <span class="md-signature"><a href="/contributor/John-Jamieson-Carswell-Smart/2756">John Jamieson Carswell Smart</a></span> <span class="md-signature"><a href="/editor/The-Editors-of-Encyclopaedia-Britannica/4419">The Editors of Encyclopaedia Britannica</a></span> </section> </section><span class="marker end-of-content"></span><span class="marker after-article"></span></div> <div id="chatbot-root"></div> </div> </div> </div> <div class="ai-dialog-placeholder"></div> </div> </div> <aside class="col-md-da-320"></aside> </div> </div> </div> </div> </article> </div> </div> </div> </div> </main> <div id="md-footer"></div> <noscript><iframe src="//www.googletagmanager.com/ns.html?id=GTM-5W6NC8" height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript> <script type="text/javascript" id="_informizely_script_tag"> var IzWidget = IzWidget || {}; (function (d) { var scriptElement = d.createElement('script'); scriptElement.type = 'text/javascript'; scriptElement.async = true; scriptElement.src = "https://insitez.blob.core.windows.net/site/f780f33e-a610-4ac2-af81-3eb184037547.js"; var node = d.getElementById('_informizely_script_tag'); node.parentNode.insertBefore(scriptElement, node); } )(document); </script>  <script> window.ap3c = window.ap3c || {}; var ap3c = window.ap3c; ap3c.cmd = ap3c.cmd || []; ap3c.cmd.push(function() { ap3c.init('ZO4siT4cLwnykPnzZWJtd3Byb2Q', 'https://engage.email.britannica.com/'); ap3c.track({v: 0}); }); ap3c.activity = function(act) { ap3c.act = (ap3c.act || []); ap3c.act.push(act); }; var s, t; s = document.createElement('script'); s.type = 'text/javascript'; s.src = "https://engage.email.britannica.com/app.js"; t = document.getElementsByTagName('script')[0]; t.parentNode.insertBefore(s, t); </script> <script class="marketing-page-info" type="application/json"> {"pageType":"Topic","templateName":"DESKTOP","pageNumber":1,"pagesTotal":15,"pageId":596034,"pageLength":755,"initialLoad":true,"lastPageOfScroll":false} </script> <script class="marketing-content-info" type="application/json"> [] </script> <script src="https://cdn.britannica.com/mendel-resources/3-133/js/libs/jquery-3.5.0.min.js?v=3.133.9"></script> <script type="text/javascript" data-type="Init Mendel Code Splitting"> (function() { $.ajax({ dataType: 'script', cache: true, url: 'https://cdn.britannica.com/mendel-resources/3-133/dist/topic-page.js?v=3.133.9' }); })(); </script> <script class="analytics-metadata" type="application/json"> {"leg":"C","adLeg":"C","userType":"ANONYMOUS","pageType":"Topic","pageSubtype":null,"articleTemplateType":"PAGINATED","gisted":false,"pageNumber":1,"hasSummarizeButton":false,"hasAskButton":true} </script> <script type="text/javascript"> EBStat={accountId:-1,hostnameOverride:'webstats.eb.com',domain:'www.britannica.com', json:''}; </script> <script type="text/javascript"> ( function() { $.ajax( { dataType: 'script', cache: true, url: '//www.britannica.com/webstats/mendelstats.js?v=1' } ) .done( function() { try {writeStat(null,EBStat);} catch(err){} } ); })(); </script> <div id="bc-fixed-dialogue"></div> </body> </html>

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Time | Definition & Facts | Britannica