Continual vs continuous – what’s the difference?

Introduction and origins

What’s the difference between continual and continuous? There’s a short answer, but it’s misleading, so – surprise! – I’m going with the long and complicated one.

Some people make a firm distinction between the two adjectives, but others don’t or only sometimes do. The distinction has merit, but it’s not categorical, more the codification of a general but lopsided pattern.

Because the words are so close in sense and use, they’re often used interchangeably (the adverbs continually and continuously even more so). This seldom leads to confusion or difficulty, but it’s also true that each word has domains it specializes in and others it’s less suited to.

Both words come from Latin continuus ‘hanging together, uninterrupted’, continual arriving via Old French continuel. Their endings, ­–al and ous, are common adjective-forming suffixes. The words’ more recent history sheds light on their use, but first let’s look at how they’re defined, since this reflects how they’re used and gets to the centre of the problem.

Definitions and history

Six major dictionaries – M-W, AHD, and Dictionary.com in US; Collins, Macmillan, and Oxford Learners in UK – each offer two definitions of continual. These vary in style and emphasis but can be condensed to: 1. recurring often; 2. continuing without interruption. Significantly, in three cases the ‘recurring’ sense comes first, in three it comes second.

A couple of dictionaries note that what is continual is often an annoyance. Later we’ll see why. Where synonyms are listed, continuous is often among them.

The same dictionaries define continuous (M-W, AHD, Dictionary.com; Collins, Macmillan, Oxford Learners) less uniformly, with 2–4 senses, some in maths or grammar. The non-technical senses centre on something continuing or being uninterrupted in space, time, extent, sequence, etc., or being connected in an unbroken line or surface.

So there’s a lot of overlap, but it’s asymmetric: continual strays into the semantic space of continuous, but the sense of ‘recurring’ is generally limited to continual. (Even so, Oxford Learners includes ‘repeated many times’ as sense #3 of 4 for continuous.)

Continuous is more physical and spatial than continual is, befitting its origins in science. Take this line in Darwin’s On the Origin of Species: ‘In most cases the area inhabited by a species is continuous.’ Robert Burchfield, for decades an editor at the OED, summarizes the two words’ historical development in his 1998 revision of Fowler’s:

Since it was first recorded in the 14C., continual has been used at all times to mean ‘incessant, perpetual’, and also, less strictly (OED), to mean ‘repeated with brief intermissions’. Continuous is a more modern word (first recorded in 1673) than continual. It was first used in technical contexts in botany (of plants having their parts in immediate connection) and optics, and was not brought into general use until the 18C.

Burchfield endorses Fowler’s original Dictionary of Modern English Usage (1926), which describes the distinction awkwardly but still fairly accurately:

That is –al which either is always going on or recurs at short intervals & never comes (or is regarded as never coming) to an end. That is –ous in which no break occurs between the beginning & the (not necessarily or even presumably long-deferred) end.

Merriam-Webster summarizes the usage dispute:

Since the mid-19th century, many grammarians have drawn a distinction between continual and continuous. Continual should only mean “occurring at regular intervals,” they insist, whereas continuous should be used to mean “continuing without interruption.” This distinction overlooks the fact that continual is the older word and was used with both meanings for centuries before continuous appeared on the scene. Today, continual is the more likely of the two to mean “recurring,” but it also continues to be used, as it has been since the 14th century, with the meaning “continuing without interruption.”

The words’ relative frequencies over the last two hundred years are shown in a curve from the Google Ngram Viewer (click to enlarge):

Google Ngram Viewer curve showing the relative frequencies of 'continual' and 'continuous' since 1800. It shows 'continual' dropping somewhat until the 20th century, then plateauing a while before climbing very slightly. 'Continuous' climbs significntly until the mid-20th century, then falls a bit but remains several times more common than 'continual'.

It’s worth comparing with data from the smaller but more reliable Corpus of Historical American English (COHA). Continual:

Bar chart from the Corpus of Historical American English showing the frequency of use of 'continual' since the 1820s. That decade is easily the highest, with the frequency declining almost uniformly per decade until the 2010s.

And continuous:

Bar chart from the Corpus of Historical American English showing the frequency of use of 'continuous' since the 1820s. It rises steadily for decades until the turn of the 20th century, plateaus a while, falls a bit, then climbs and falls unpredictably until the present day.

Collocations and synonyms

We can get an idea of the adjectives’ favoured contexts by examining their collocates – the words they tend to occur beside. To do this, I looked at a few of Mark Davies’ contemporary and historical language corpora.

iWeb shows continual collocating mostly with improvement, basis, growth, process, use, learning, development, service, improvements, professional, support, change, and monitoring. It shows continuous collocating with improvement, integration, shooting, use, delivery, process, learning, flow, monitoring, operation, service, basis, and development.

Lots of overlap, then, and both words occur most commonly in a fairly narrow contextual range. GloWbE shows similar patterns.

COHA’s older data set shows continual collocating mostly with change, struggle, state, source, presence, stream, effort, motion, changes, danger, agitation, fear, succession, conflict, flow, and dread. It shows continuous collocating with line, action, stream, flow, process, series, succession, improvement, roar, operation, service, spectrum, session, development, supply, and motion.

Again there’s overlap, but notice that continuous, reflecting its scientific origins, has traditionally tended to partner words that are more physical and less abstract. We can also see, underlined, some negative words collocating frequently with continual, hence its connotations of annoyance reported in some dictionaries.

Because of their lack of symmetry, Burchfield recommends using synonyms outside of technical contexts: ‘recurrent or intermittent instead of continual, and unbroken, uninterrupted, or incessant instead of continuous.’ Larry Trask, in Mind the Gaffe, offers similar advice. But this will be heeded only by some of those concerned about the potential for confusion, which most people aren’t.

Trask calls the distinction ‘subtle but clear’, but it’s not always obvious which word best fits a given activity. Would we say a busy receptionist handles phone calls non-stop despite lulls? That a week of heavy rain is incessant even if there are breaks? Many would. It can depend, as Merriam-Webster’s Pocket Guide to English Usage says, ‘on whether a given writer perceives the activity as interrupted or not’.

The prescriptive rule and its status

When two words are so similar in sense, there arises in certain personality types an urge to separate them categorically, the better to order the language. With continual/continuous the Merriam-Webster Dictionary of English Usage (MWDEU) dates this trend to Elizabeth Jane Whately’s Collection of English Synonyms (1851), which assigned the ‘recurring’ sense to continual and ‘uninterrupted’ to continuous.

Prescriptive guides have upheld this distinction ever since. Here’s the influential Chicago Manual of Style in the US: ‘What is continual is intermittent or frequently repeated. What is continuous never stops—it remains constant or uninterrupted.’ And its UK equivalent, the New Oxford Style Manual: ‘continual: constantly or frequently occurring; continuous: without interruption, unbroken’.

This neat division is echoed continuously – continually, if you prefer – in dozens of usage books. Laurence Urdang’s Dictionary of Differences says the words are ‘discriminated in good style’, yet one of his examples – ‘continuous hiccuping’ – is debatable per the rule he advocates. Webster’s Compact Dictionary of Synonyms uses watery images to delineate the words’ scope:

Continual implies a close prolonged succession or recurrence <continual showers the whole weekend>. Continuous usually implies an uninterrupted flow or spatial extension <the continuous roar of the falls>.

Photo showing the surface of water and nothing else, going from white and light blue at the top to dark blue at the bottom. Small waves are interspersed with countless small ripples.

Are these ripples on the surface of Galway Bay continual or continuous?

The Columbia Guide to Standard American English illustrates the distinction with gunfire:

A continual annoyance is one that goes on repeatedly, as in Continual bursts of gunfire kept us awake all night. Presumably it was intermittent, with silences between bursts. Continuous works in either time or space and means “unending, without interruption.” Continuous gunfire would not cease even for a moment.

Take a moment, if you like, to process the characterization of all-night gunfire as an ‘annoyance’.

Garner’s Modern English Usage refers to the words as ‘frequently confused’. But given their long-entangled usage, can we assume confusion in people who don’t observe the rule in its strictest form? Jane Austen wrote about ‘a continual state of Inelegance’; R. L. Stevenson, in Treasure Island, described a breeze sprinkling the floor with ‘a continual rain of fine sand’.

Both examples are from MWDEU, which says continual is ‘more likely’ than continuous to be used for ‘repetition of something that may be interrupted’, and that continuous, unlike continual, ‘is used of continuity in space’ – Samuel Johnson noted this too – and retains technical uses in maths, biology, etc. But both words, MWDEU says, are routinely used in similar contexts:

Because it has a much broader spectrum of application, continuous is the more common word. Yet, continual has been used since the 14th century in its primary sense of “continuing indefinitely in time without interruption” and is still used in that sense. Continuous is more recent in this application, having become established in it only in the 1830s, but it is very frequently so used in current English. Continual is the word most often chosen when the meaning is “recurring”. It is possible for you to follow Miss Whately’s distinction or one of its modern versions, and many good writers do so. Others equally good do not, however.

The adverbs

The adverbs are less complicated, but also less neat than sticklers would prefer. Mirroring the adjectives, continually arrived in the early 14thC, continuously in the late 17thC. In the intervening centuries, continually did its double duty as both ‘incessantly, constantly’ and, less strictly (OED), ‘with frequent repetition’.

Burchfield picks up the story:

The arrival of continuously signalled a fairly general restriction of continually to the less strict meaning. From the 18C. onward, continuously has tended to be the more dominant word of the two, esp. when the unbroken nature of a process (in space or time) or set of events (e.g. unbroken terms of office) is being stressed.

But he notes that good writers often use the adverbs more or less interchangeably, depending on the degree to which continuity is being emphasized. At the moment they occur at roughly the same frequency (at least in the Google Books corpus, to which caveats apply):

Google Ngram Viewer curve comparing the use of 'continually' and 'continuously' since 1800. It shows 'continually' declining steadily until the mid-20th century, then recovering a little, and 'continuously' rising steadily until the mid-20th century, then falling a little, so that they two words are now about equal in frequency in the Google Books corpus.

MWDEU finds it ‘very difficult to discern a marked difference’. But its files show that continuously ‘does all the technical work’ and is used ‘when something continues in space rather than time’, to stress that something happens steadily rather than episodically, and to stress ‘an unbroken succession of discrete time periods’.

Continually, per MWDEU, is used especially ‘when something continues to exist or happen, with or without interruptions, for an indefinite period’, or ‘when repetition is emphasized’, as in Muriel Spark’s reference to rereading certain works continually. It says its examples

show uses of continually and continuously in which a fastidious writer can make a rational choice. But these do not represent all usage. Many times the words are used as if they were interchangeable.

Per MWDEU, it’s usually continuously that encroaches where continually ‘would have worked as well and might have been expected’, rather than the other way around. This, it says, probably owes to the steady increase in use of continuous and continuously ‘rather than the result of confusion, indifference, or a failure of standards’.

Others would attribute the encroachment to precisely those elements. You get to decide where your sympathies lie.

Concluding advice

If you want to apply the distinction but you struggle to remember it, try a mnemonic. Continuous ends in an ‘s’, which is like a river flowing without interruption. Continual forms the adverb continually, whose ‘ll’ shows the intermittent repetition invoked. Garner suggests “one uninterrupted sequence” for continuous.

In formal contexts it’s worth at least being aware of the distinction sometimes preferred, and you may take satisfaction in observing it. In everyday usage it’s unlikely to matter: you can trust your hunch or sprachgefühl, mindful that a few listeners or readers will notice, or you can apply the rule, mindful that many won’t.

*

Many ‘confusables’ are less messy than continual and continuous. I’ve written previously about complement and compliment, defuse and diffuse, discreet and discrete, flaunt and flout, militate and mitigate, peak, peek, and pique, pore and pour, principal and principle, refute and reject, stationary and stationery, and who’s and whose.

6 Responses to Continual vs continuous – what’s the difference?

  1. John Cowan says:

    In some places, gunfire (into the air) is used as a form of celebration, and after all fireworks and rocketry are two different applications of the same technology.

    I note that incessant actually has the same ambiguity: the OED defines it as ‘continual, either in duration or repetition’. Shakespeare seeks of “the incessant weeping of my wife”, which can be at most continual, whereas Dryden’s “incessant noise like that of a water mill” is more likely to be continuous. So using ‘incessant’ to define either sense isn’t all that helpful, though people do.

    • Stan Carey says:

      Good point about incessant. Some works that treat continual and continuous discuss incessant alongside them (or constant or some other synonym). Webster’s Compact Dictionary of Synonyms, for example, treats all of the above together, plus perpetual and perennial. It describes incessant as implying ‘ceaseless or uninterrupted activity <the incessant quarreling frayed her nerves>’. But this too is rather ambiguous and subjective.

      That’s true about gunfire, of course. I think I’d still find all-night celebratory gunfire more than just annoying, though.

  2. astraya says:

    I suspect I don’t say/write continual(ly) much. The closest thing I have to a personal corpus is my diary of my first stay in Korea (2006-09). There are five occurrences of continuous(ly), being the grammar terms present and past continuous, a day of ‘continuous frustration’, a rotating air vent which made ‘a continuous screeching noise’ and a description of the cable car at Hong Kong Ocean World, which ‘is meant to move continuously, but sometimes stops without warning’. On the other hand, the only occurrence of continually is in an article I quoted about historical authenticity: sailing ships like HMS Victory had carpenters who were “continually making repairs and modifications”.

    • Stan Carey says:

      Thanks for checking your own usage. It looks like your use of the words, however rare, accords with the distinction sometimes made. I don’t use them much either. In 13 years on Twitter, excluding third-party quotations, I’ve used continually once, referring to the use of short sentences in a text, and I once described a word being in continuous use since the 15th century. A 100k-word travelogue I wrote in my 20s contains no occurrence of the adjectives or the adverbs at all. And in Gmail I haven’t used either word in years, though I found mention of “the idea of a consistent, continual self”, jobs “arriving continuously”, and making social media coverage of a topic “as broad and continuous as possible”; one or two of these might be cavilled at. It would be great to have an automatically updated corpus of one’s language use in all domains.

      • astraya says:

        I also checked my blog post draft document, which covers a longer period but is more constrained in its vocabulary. Along multiple occurrences of the grammatical term, there is one occurrence of continuous (the second, public rehearsal of the opening ceremony of the Sydney Olympics was ‘essentially continuous’) and none of continual(ly). Probably not a lot can be concluded from that, but it doesn’t contradict what I found in my Korea diary.
        When the great conspiracy microchips us all, maybe one of the benefits to linguists will be a corpus of what everyone says. Or maybe eventually what everything thinks.
        Do you know of any tool which will count the number of different words in any given text? That might of limited value because most of the words will be ‘the’, ‘and’ and ‘I’ etc. The next step would be to rank each of the words in any given text with an overall ranking of word counts in various genres. Do I or any other writer (over-)use any particular words?

        • Stan Carey says:

          I remember reading about research into the frequency of swearing in which people hung recorders around their necks for days (or was it weeks?) on end. But then that all needs to be transcribed, proofread, and coded. I know that automated transcription software has come on a lot in recent years, but we’re still a ways off the full package of automated real-time speech to POS-tagged corpus.

          I suspect that everyone overuses certain words, at least in the sense that they use certain words, phrases, or constructions more than average and in a signature way: enough to produce a basis for stylistics, forensic linguistics, etc.

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