The evolution of the past tense – how verbs change over time

In Chaucer’s time, English had many more irregular verbs than now.For decades, scientists have realised that languages evolve in strikingly similar ways to genes and living things. Their words and grammars change and mutate over time, and new versions slowly rise to dominance while other face extinction.

In this evolutionary analogy, old texts like the Canterbury Tales are the English language’s version of the fossil record. They preserve the existence of words that used to be commonplace before they lost a linguistic Darwinian conflict with other, more popular forms.

Now, Erez Lieberman, Martin Nowak and colleagues from Harvard University are looking at this record to mathematically model how our verbs evolved and how they will change in the future.

Regularity and irregularity

Today, the majority of English verbs take the suffix ‘-ed’ in their past tense versions. Sitting alongside these regular verbs like ‘talked’ or ‘typed’ are irregular ones that obey more antiquated rules (like ‘sang/sung’ or ‘drank/drunk’) or obey no rules at all (like ‘went’ and ‘had’).

In the Old English of Beowulf, seven different rules competed for governance of English verbs, and only about 75% followed the “-ed” rule. As the centuries ticked by, the irregular verbs became fewer and far between. With new additions to the lexicon taking on the standard regular form (‘googled’ and ‘emailed’), the irregulars face massive pressure to regularise and conform.

Today, less than 3% of verbs are irregular but they wield a disproportionate power. The ten most commonly used English verbs – be, have, do, go say, can, will, see, take and get – are all irregular. Lieberman found that this is because irregular verbs are weeded out much more slowly if they are commonly used.

Many irregular verbs have regularised since Beowulf’s timeTo get by, speakers have to use common verbs correctly. More obscure irregular verbs, however, are less readily learned and more easily forgotten, and their misuse is less frequently corrected. That creates a situation where ‘mutant’ versions that obey the regular “-ed” rule can creep in and start taking over.

The mathematics of verbs

Lieberman charted the progress of 177 irregular verbs from the 9th century Old English of Beowulf, to the 13th century Middle English of Chaucer’s Canterbury Tales, to the modern 21st century English of Harry Potter. Today, only 98 of these are still irregular; many formerly irregular verbs such as ‘laugh’ and ‘help’ have put on new regular guises.

He used the CELEX corpus – a massive online database of modern texts – to work out the frequency of these verbs in modern English. Amazingly, he found that this frequency affects the way that irregular verbs disappear according to a very simple and mathematical formula.

They regularise in a way that is ‘inversely proportional to the square root of their frequency’. This means that if they are used 100 times less frequently, they will regularise 10 times as fast and if they are used 10,000 times less frequently, they will regularise 100 times as fast.

As Lieberman says, “We measured something no one really thought could be measured, and got a striking and beautiful result.” Using this model, the team managed to estimate how much staying power the remaining irregular verbs have and assigned them ‘half-lives’ just as they would to radioactive isotopes that decay over time.

Verbs of the future

The two most common irregulars – ‘be’ and ‘have’ – crop up once or more in every ten words and have half-lives of over 38,000 years. That’s such a long time that they are effectively immune to regularity and are unlikely to change.

Several more irregular verbs will have changed by the time the next edition of the Oxford English Dictionary is publishedLess common verbs like ‘dive’ and ‘tread’ only turn up once in every 10,000-100,000 words. They have much shorter half-lives of 700 years and for them, regularisation is a more imminent prospect. Out of the 98 remaining irregular verbs examined in the study, a further 16 will probably have adopted the ‘-ed’ ending by 2500.

Which will be next? Lieberman has his speculative sights set on ‘wed’. It is one of the least commonly used of modern irregular verbs and the past form ‘wed’ will soon be replaced with ‘wedded’. As he jokes, “Now is your last chance to be a ‘newly wed’. The married couples of the future can only hope for ‘wedded’ bliss.

That little jibe highlights the greatest strength of this paper – it’s not the striking and elegant results, it’s Lieberman’s delightful turns of phrase. Suitably for a study about language, he describes his results in pithy and measured language. Observe, for example, his concluding paragraph:

“In previous millennia, many rules vied for control of English language conjugation and fossils of those rules remain to this day. Yet, from this primordial soup of conjugations, the suffix ‘-ed’ emerged triumphant. The competing rules are long dead, and unfamiliar even to well-educated native speakers. These rules disappeared because of the gradual erosion of their instances by a process that we call regularisation. But regularity is not the default state of a language – a rule is the tombstone of a thousand exceptions.”

Ah, if only all scientists could write with such poetic flair.

For more on the evolution of language, I highly recommend the excellent blog Babel’s Dawn by Edmund Blair Bolles.


Reference: Lieberman, Michel, Jackson, Tang & Nowak. 2007. Quantifying the evolutionary dynamics of language. Nature doi:10.1038/nature06137


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9 Responses

  1. Ed: Thank you very much for this enlightening post. I’m going to return to it again for greater understanding.

    I’ve always been fascinated by the way language has evolved: most Indian languages and English too, are offshoots of Indo-European ancestry. All this makes for fascinating research as these Harvard folks have shown.

    I’ll get to the Babel’s Dawn blog soon. Is it going to be one of the Intellectual Blogger Awardees from you? :-)

  2. Hi Mahendrap,

    Have a look at books by Steven Pinker for some great reads on language evolution.

    And thanks for reminding me that I have to choose some Intellectual Blogger nominees soon – I haven’t forgotten, but most of the blogs I read are science ones and because of my mission statement, I want to specifically recommend ones that are written for lay readers…

  3. Oddly enough, I got here via Google while trying to see if anyone besides me had noticed that the “ed” seems to be disappearing.

    People almost never write “used to” — it’s always “use to”, but that’s just the beginning. A restaurant marquee reads “experience kitchen help needed.” Someone writes “we’re going to have grill fish tonight.”

    My own observation is that many verbs are becoming irregular.

  4. People almost never write ‘used to’?? I’m not sure who these people are but they’re not one’s whose writing I read… All the instances you’ve highlighted are cases of verbs being used wrongly! And yes, there is an argument that incorrect use that becomes widespread could be the grammar of tomorrow but I highly doubt that those mistakes are common enough to trigger such a transition.

  5. This is yet another example of mathematicians and programmers trying to explain away the complex humanity of linguistics and failing. I hate to be a poopooer on the parade but I can state with certainty that theories like these simply lack the level of multi-dimensional sophistication to predict anything that will motivate a normal human language to change such as:

    1. social-dependent trends and preferences
    2. important changes in politics and alliances
    3. wars and other culture-shattering tragedies
    4. technological changes that affect terminology and the ways we communicate

    It’s an interesting idea in a very loose sense of the word, but hardly a scholarly theory. This is more money and time being wasted on superficial nonsense for the sake of marketed sensationalism. It may very well appeal to the masses (to my chagrin), but it’s still vacuous in the end and unbecoming of a university like Harvard to be involved with, I feel. This has the lofty air of answering something but logically speaking can’t possibly answer anything at all.

  6. Glen, why don’t you take a look at the mission statement on the top left and see if, with your clearly vast vocabulary, you understand the word ‘elitism’. Because your post and general demeanour is rife with it. Quite frankly, you’re a fine one to be accusing someone else of having a ‘lofty air’.

    This is histrionic foot-stomping at best. Did you take the time to read the paper? Did you actually look at the data and analyse it? Or did you in fact take umbrage at the very thought that someone could be trying to understand your precious language with mathematics?

    “Explain away the complex humantiy of linguistics”? Where exactly was this done? The study aimed to measure the regularisation rates of verbs, nothing more. As it is, they found that it happened with a nice mathematical model. Obviously, other variables like the ones you mentioned will have an effect, but this doesn’t change the fact that there might be underlying patterns.

    If you think that the relationship they found is invalid, why not have a crack at critiquing the data or their methods? As it is, you appear to be saying: “Their results are wrong, because they couldn’t possibly be right.” That’s not science, that’s lazy, facile snobbery.

    If anything, the paper and the author’s comments are overflowing with a love of the English language and a desire to understand it further. Your comments on courting sensationalism are speculative and those about money are daft – does this seem like an expensive project?

    Lieberman et al. should be commended for their interesting study and the beautiful way they wrote it up. If you don’t like the conclusions, review the data and come up with a proper rebuke that’s not an ill-considered pretentious rant. And if you’d like to do all of that elsewhere, that would be smashing.

  7. Another superb article. It is excellent that some people have taken the time and effort to do the maths – essentially the hard evidence of statistics helps to “prove” and quantify the evolution of language. It helps when they write it up so eloquently too.

    It may have a different mechanism, but if only more people could simplify and disseminate the statistics on genetic evolution too …

  8. [...] For more on the evolution of language, have a look at this post on the evolution of the past tense in English verbs. [...]

  9. Neat, concise presentation of the issues! If changes in language over time can be represented by mathematical formulae, it makes you wonder what other aspects of human behaviour might be susceptible to the same treatment? Fashion? Morals?
    It also makes me worry that verbbusters is going to become redundant.

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