2.2 Interactions Between Regularity and Irregularity

As we put forward in our introduction part，linguistic concerns have long covered these questions：What is the nature of regularity and irregularity?By what criteria do we tell regulars from irregulars?What might be the interaction between the two since regulars and irregulars coexist in certain grammatical fields?Do the two always keep constant or changing?

2.2.1 The Nature of Regularity and Irregularity

It has been taken for granted that the nature of regularity and irregularity mainly depends upon the nature of inflection，which can be phonologically as well as morphologically regular or irregular.So the role of regular inflection has thus been widely regarded as a default operation in dividing regular forms from irregular ones.Many languages contrast regular（e.g.，rat-rats）and irregular（e.g.，mouse-mice）processes of inflection（Pinker,1991,1999）.Regular and irregular inflections differ in their sensitivity to memorized forms.The application of regular inflection is general：It is easily applied to rare words，whose memory trace is weak（Gordon&Alegre,1999；Ullman,1999），and to novel words that do not resemble any existing words in memory and hence cannot get an inflected form by analogy（Berent，Pinker&Shimron,1999；Prasada&Pinker,1993）.In contrast，irregular inflection is highly dependent on memorized forms：Most irregulars are frequent，the rarer ones are likely to be regularized（Marcus，Pinker，Ullman，et al.1992；Bybee,1985），and people are unlikely to apply an irregular pattern to a novel word unless it is highly similar to an existing irregular（Berent et al.,1999；Bybee&Moder,1983；Prasada&Pinker,1993）.There are also various grammatical processes that are selective with respect to regularity.For example，names take regular but not irregular inflection despite their similarity（or even identity）to existing irregular words（e.g.，Julia and her husband are the Childs，not the Children；see Marcus et al.,1995；Kim，Marcus，Pinker，et al.1994）.Conversely，compounds selectively admit irregular，but not regular plurals（cf.mice-earters vs.rats-eaters，e.g.，Alegre&Gordon,1996；Gordon,1985）.The distinction between regular and irregular inflection is further evident in on-line priming effects（e.g.，Kempley&Morton,1982；Münte，Say，Clahsen，et al.1998；Stanners，Neiser，Hernon，et al.1979），developmental patterns（e.g.，Marcus，Pinker，Ullman，et al.1992），genetic disorders（Clahsen&Almazen,1998；Ullman&Gopnik,1999）and neurological dissociations（e.g.，Marslen-Wilson&Tyler,1997；Ullman，Berdiga&O'Craven,1997）.

It is evident that languages like English confound the morphological properties of regular and irregular forms with their phonological characteristics.For instance，regular plurals tend to faithfully preserve the base's phonology（e.g.，rat-rats），whereas irregular nouns tend to alter it（e.g.，mouse-mice）.The distinction between regular and irregular inflection may thus be an epiphenomenon of phonological faithfulness （Prince&Smolensky,1997；Benua,1997）.Regular inflection as in rat-rats invariably attaches a consonantal suffix to the singular base and it does not modify the stem's phonological form.Regular inflection is thus phonologically“faithful”to the base.In contrast，irregular inflection as in mouse-mice tends to be phonologically unfaithful to the base，altering the base's phonological structure，primarily its vowels.This systematic confound raises the concern that morphological regularity is an epiphenomenon of phonological faithfulness（Rueckl，Mikolinski，Raveh，et al.1997；Stemberger,1998）.

Inflection is the morphological realization of features that are obligatory parts of linguistic expressions.For instance，sentences must carry tense；so tense morphemes are the overt realization of verbs.Nouns need to be specified for either plural or singular；so number marking is the overt realization of nouns.Adjectives and adverbs may vary in three degrees.So degree marking is the overt realization of adjectives and adverbs.Inflection is completely productive；there are no verbs that resist tense marking.Inflection never changes the category of the word.For example，verbs stay verbs，and nouns stay nouns.

Derivation，in nature，is also the morphological realization of certain features of linguistic expressions，but does not have the same kind of obligatory nature as inflection.For example，verbs do not in general have to be marked for whether they describe an event that has already occurred before.Thus the re-prefix is not part of the inflectional system of English.Derivation has the potential to change the category of a word.Derivational affixes may have limited productivity.For instance，not all adjectives combine with-ize（*lawfulize）.

Though these phonological confounds complicate the interpretation of morphological regularity effects in English，they cannot，at present，explain all of these effects.A few irregular forms in English do preserve the stem faithfully，yet they follow the same grammatical constraints as irregular forms that change the stem.For example，irregular oxen preserves the stem ox，unlike mouse-mice and tooth-teeth，yet all three behave the same in regard to being admissible in compounds（compare oxen power with*horses power，a contrast identical to mice-infested versus*rats-infested and teethmarks versus*clawsmarks）.Similarly，the irregular participle shaken preserves the stem shake，yet it behaves just like stem-changing irregular participles in being regularized when the stem is derived from a noun.Just as one says ringed the city（“form a ring around”），not rang，one says I can't have any more milkshakes；I'm shaked out（“had too many shakes”），not shaken（Kim et al.,1992）.Moreover，this regularization effect holds across a wide variety of phonological patterns relating irregular past or participle effects to their stems stick-stuck versus high-sticked（“hit with a stick”）；no change：cost-cost versus costed（“computed the costs”）；vowel-change plus suffix：mean-meant versus meaned（“computed the mean”）；rime replacement：standstood versus grandstanded（“play to the grandstand”）；suppletion：be-was versus to-be-or-not-to-be'd（“recited‘to be or not to be’”）.For experimental data，attested citations from speech，and additional examples，see Pinker（1999，Chapter 6）."/>.Though it is unlikely that phonological confounds can account for all the phenomena related to regularity in English，the confound does raise an important and unanswered theoretical question：How does the regularity of an inflectional process depend on the phonological correspondence between the base and the inflected form?Specifically，does the role of regular inflection as a default require phonological faithfulness?

2.2.2 Systematic Regularization of Irregulars

An intriguing aspect of inflection is that irregular forms can sometimes turn up in regular form.Some of these regularizations are unsystematic.For example，doublets such as dived/dove and dreamt/dreamed，in which the regular forms are used sporadically because the irregular forms are low in frequency and hence poorly remembered.But many are systematic：in particular contexts，the regular forms are consistently used，in which their standard irregular forms seem to be grammatically unacceptable.Here are some examples of the phonomena of systematic regularization of irregulars：

（1）All my daughter's friends are low-lifes（*low-lives）.

（2）I'm sick of dealing with all the Mickey Mouses in this administration（*Mickey Mice）.

（3）Boggs has singled，tripled，and flied out（*flown out）in the game so far.

The phenomenon immediately shows that sound alone cannot be the input to the inflectional system.In the last example，a given sound，such as fly，can be mapped onto flew and flown when referring to birds but flied when referring to baseball players.The question is：what is the extra input causing the shift?

Many psychologists，connectionists，and prescriptive grammarians have suggested that the missing input features are semantic：when a verb is given a new extended or metaphorical meaning，extra features for that meaning are activated，making the new verb less similar to its predecessor and decreasing activation of the associated irregular form（Kim，Pinker，Prince，et al.1991；Kim，Marcus，Pinker，et al.1994）.This explanation，however，is clearly false；most semantic modifications in fact leave an irregular verb's inflectional forms intact.Here are some examples：

（4）Prefixing：overate/*overeated，overshot/*overshooted，outdid/*outdoed，preshrank/*pre-shrinked.

（5）Compounding：workmen/*workmans，superwomen/*superwomans，muskoxen/*muskoxes］，stepchildren/*stepchilds，milkteeth/*milktooths.

Metaphor：straw men/*mans，snowmen/*snowmans，God's children/

*childs，sawteeth/*sawtooths，six feet/*foots long.

（6）Idiom：cut/*cutted a deal，took/*taked a leak，bought/*buyed the farm，caught/*catched a cold，hit/*hitted the fan，blew/*blowed him off，put/*putted him down，came/*comed off well，went/*goed nuts.

These examples show that merely adding semantic features to a pattern associator，in the hopes that the resulting unfamiliarity of new combinations will inhibit highly trained irregular responses，is unlikely to handle the phenomenon.

2.2.3 The Right-Hand-Head Rule

The Words-and-Rules theory explains this phenomenon by using an independently motivated theory of compositionality in word-formation（Pinker&Ullman,2002）（see also Figure 2.3）.Irregular-sounding words are regularized if they lack a root in head position that can be marked for the inflectional feature（tense or number）.The regular suffix applies as the default，as it does in other cases where memory access is disabled.Paul Kiparsky（1982）and Edwin Williams（1981）try to explain this phenomenon by using a principle，sometimes called the Right-Hand Head Rule，which formulates that a new complex word inherits its properties from the properties that are stored in the memory entry of the rightmost morpheme—the“head”—including any irregular forms.The pipeline of information from the memory entry of the head at the bottom of the tree to the newly created complex lexical item symbolized by the node at the top of the tree can be schematized as follows：

As with syntax in general，the syntax of words encompasses a scheme by which the properties of a novel combination can be predicted from the properties of its parts and the way they are combined.Consider the verb overeat.It is based on the verb root eat：The root is then joined with a prefix，yielding the following structure：

The result is a new word that has inherited its properties from the properties of the rightmost morpheme inside it，in this case，eat.What syntactic category（part of speech）is overeat?It is a verb，just as eat is a verb.What does overeat mean?It refers to a kind of eating—eating too much—just as eat refers to eating.And what is its past tense form?Overate，not overeated，just as the past tense form of eat is ate，not eated.

Another example is the compound noun workman which is formed by prefixing the noun man by the verb work：

Once again，its properties are inherited from man，its rightmost morpheme or head.Workman is a noun，just as man is a noun；it refers to a kind of man，just as man refers to a man，and its plural form is irregular workmen，because the plural form of man is irregular men（Pinker,1999）.

The explanation for systematic regularization is that some complex words are exceptional in being headless.That is，they don't get their properties，such as grammatical category or referent，from their rightmost morpheme.The normal Right-Hand-Head rule must be turned off for the word to be interpreted and used properly.As a result，the mechanism that ordinarily retrieves stored information from the word's root is inactive，and any irregular form stored with the root is trapped in memory，unable to be passed upward to apply to the whole word.The regular rule，acting as the default，steps in to supply the complex word with a past tense form，undeterred by the fact that the sound of the word ordinarily would call for an irregular form.

Here is how the explanation works for one class of regularizations，compounds whose referent is rather than an example of the referent of the rightmost morpheme.For example，a low-life is not a kind of life，but a kind of person，namely，a person who has or leads a low life.For it to have that meaning，the Right-Hand-Head Rule，which would ordinarily make low-life mean a kind of life（the semantic information stored in memory with life），must be abrogated.With the usual data pipeline to the memory entry for the head disabled，there is no way for the other information stored with life to be passed upward either，such as the fact that it has an irregular plural form，lives.With the irregular plural unavailable，the regular-s rule steps in，and we get low-lifes.

Similar logic explains regularized forms such as still lifes（a kind of painting，not a kind of life），saber-tooths（a kind of cat，not a kind of tooth），flatfoots（policemen，not feet），bigmouths（not a kind of mouth but a person who has a big mouth），and Walkmans（not a kind of man，but a“personal stereo”）.This effect has been demonstrated in experiments in which four-to-eight-year-old children are presented with“has-a”compounds，such as snaggletooth，and asked to pluralize them.They provide regular plurals at a significantly higher rate than when they pluralize ordinarily novel compound nouns with irregular roots（Kim et al.,1994）.The same explanation works for a second class of regularizations，eponyms.We hear Mickey Mouses because the ordinary noun mouse was converted to a distinct syntactic category，that for names，when Walt Disney christened his animated murine hero.（Names are syntactically distinct from common nouns，and hence must bear a different lexical category label，possibly“NP”，possibly a category specific to proper names.For present purposes，it suffices to symbolize that category simply as“name”（Marcus et al.,1995）.Then in colloquial speech the name Mickey Mouse was converted back into a common noun，a Mickey Mouse，referring to a simpleton：

The new noun is headless，because the Right-Hand-Head Rule had to be turned off twice to convert the noun“mouse”into a name，and then to convert the name back into a noun，both violations of the usual upward-copying process.With that process disabled，the irregular plural“mice”remains unexamined in the lexicon，and the regular suffixation rule fills the vacuum and yields Mickey Mouses.The same explanation works for most other pluralized irregular-sounding eponyms：

（7）The Toronto Maple Leafs/*Leaves（a hockey team named after Canada's national symbol，The Maple Leaf）.

（8）Renault Elfs/*Elves（cars）.

（9）Michael Keaton starred in both Batmans/*Batmen（movie titles）.

（10）We're having Julia Child and her husband over for dinner.You know，the Childs/*Children are really great cooks.

As before，this effect has been shown to work in the language production of children（Kim et al.,1994）.

The explanation works in the verb system as well，in the class of regularized past tense and past participle forms of denominal verbs：verbs that have been formed out of nouns.In baseball，the verb to fly was converted over a century ago into a noun，a fly，referring to a high arcing ball.The noun was then converted back into a verb，to fly out，meaning“to hit a fly that is caught.”

The verb root to fly is thus sealed off from the derived verb to fly out at two layers of the structure，the one that converted the verb root to a noun（i.e.，failed to copy upwards the information the root's category is“verb”），and the one that converted the noun back into a verb.

Among baseball cognoscenti who can sense the fly ball in flying out，the irregular forms flew and flown are unable to climb out of the lexical entry for fly，and-ed applies as the last resort，yielding flied out.The same explanation works for other denominals，such as high-sticked/*high-stuck（hit with a high stick，in hockey），grandstanded/*grandstood（played to the grandstand），and ringed/*rang the city（formed a ring around）.This regularization process can be documented experimentally in adults'and children's attempts to form past tenses of new verbs（Kim et al.,1994）.Similar explanations may be applied to four other kinds of rootless or headless derivation（Marcus et al.,1995）：

（11）Onomatopoeia：The engine pinged/*pang；My car got dinged/*dang.

（12）Quotations：While checking for sexist writing，I found three“man”s/*“men”on page 1.

（13）Foreign Borrowing：succumbed/*succame；derided/*derode；chiefs/*chieves；gulfs/*gulves（all borrowed from French or Latin）.

（14）Artificial concoctions（truncations，acronyms）：lip-synched/*

lip-sanch（from synchronize；Ox's/*Ox-en（hypothetical abbreviation for containers of oxygen）.

Though regular forms can appear in many contexts that are closed to the irregulars，there is one circumstance in which the reverse is true：inside compound words.An apartment infested with mice may be called mice-infested（irregular plural inside a compound），but an apartment infested with rats is called not*rats-infested（regular plural inside compound）but rat-infested（singular form inside compound），even though by definition one rat does not constitute an infestation.Note that there is no semantic difference between mice and rats that could account for the grammaticality difference；it is a consequence of sheer irregularity.Similar contrasts include teethmarks versus*clawsmarks，men-bashing versus*guys-bashing，and purple-people-eater versus*purple-babies-eater.In experiments in which subjects must rate the naturalness of novel compounds，Anne Senghas，John Kim（Senghas，Kim&Pinker,1991）have found that people reliably prefer compounds with irregular plurals，such as geese-feeder，over compounds with regular plurals，such as ducks-feeder，and that the effect is not a by-product of some confounded semantic，morphological，or phonological difference between regular and irregular plurals（Pinker,1999）.

A simple explanation，based loosely on Kiparsky（1982），might run as follows.Morphological composition of words takes place in several stages.There is a lexicon of memorized roots，including irregular forms.That lexicon supplies the input to rules of regular derivational morphology，which creates complex words（including compounds）out of simple words and morphemes，outputting a stem.Stems are then inputted to a third component，regular inflection，which modifies the word according to its role in the sentence.In simplified form，the architecture of morphology would look like this：

The word mice，stored as a root in the first component，is available as an input to the compounding process in the second component，where it is joined to infested to yield mice-infested.In contrast，rats is not stored as a memorized root in the first component；it is formed from rat by an inflectional rule in the third component，too late to be inputted to the compounding rule in the second.Hence we get rat-infested but not rats-infested.

Peter Gordon（1985）showed that 3-5-year-old children are sensitive to this principle.He asked them questions such as，“Here is a monster who likes to eat X.What would you call him?”First he trained them on mass nouns such as mud，which don't take a plural，to introduce them to the compound construction，in this case mud-eater，without biasing their subsequent answers.Then he tested them by asking what they would call a monster who likes to eat rats.The children virtually always said rat-eater，not rats-eater.In contrast，they frequently called a monster who likes to eat mice a mice-eater and those children who occasionally used the overregularized plural mouses in other contexts never used it in a plural such as mouses-eater.In an interesting twist，Gordon checked to see whether children had had an opportunity to learn the distinction by noticing irregular-plural-containing-compounds in their parents'speech，such as teethmarks，and simultaneously noticing the absence of regular-plural-containing-compounds in their parents'speech，such as clawsmarks.He found that neither kind of plural is common enough in English for children to have reliably heard them；virtually all commonly used compounds take a singular first noun，such as toothbrush.Therefore children's sensitivity to the teethmarks/clawsmarks distinction is likely to be a product of the innate architecture of their language system，not a product of a tabulation of occurring and non-occurring forms in parental speech（Pinker,1999）.