Inflecting Plurals

All of the "PL_..." plural inflection subroutines take the word to be inflected as their first argument and return the corresponding inflection. Note that all such subroutines expect the singular form of the word. The results of passing a plural form are undefined (and unlikely to be correct).

The "PL_..." subroutines also take an optional second argument, which indicates the grammatical "number" of the word (or of another word with which the word being inflected must agree). If the "number" argument is supplied and is not 1 (or "one" or "a", or some other adjective that implies the singular), the plural form of the word is returned. If the "number" argument does indicate singularity, the (uninflected) word itself is returned. If the number argument is omitted, the plural form is returned unconditionally.

The various subroutines are:

"PL_N($;$)"

The exportable subroutine "PL_N()" takes a singular English noun or pronoun and returns its plural. Pronouns in the nominative ("I" -> "we") and accusative ("me" -> "us") cases are handled, as are possessive pronouns ("mine" -> "ours").

"PL_V($;$)"

The exportable subroutine "PL_V()" takes the singular form of a conjugated verb (that is, one which is already in the correct "person" and "mood") and returns the corresponding plural conjugation.

"PL_ADJ($;$)"

The exportable subroutine "PL_ADJ()" takes the singular form of certain types of adjectives and returns the corresponding plural form. Adjectives that are correctly handled include: "numerical" adjectives ("a" -> "some"), demonstrative adjectives ("this" -> "these", "that" -> "those"), and possessives ("my" -> "our", "cat's" -> "cats'", "child's" -> "childrens'", etc.)

"PL($;$)"

The exportable subroutine "PL()" takes a singular English noun, pronoun, verb, or adjective and returns its plural form. Where a word has more than one inflection depending on its part of speech (for example, the noun "thought" inflects to "thoughts", the verb "thought" to "thought"), the (singular) noun sense is preferred to the (singular) verb sense.

Hence "PL("knife")" will return "knives" ("knife" having been treated as a singular noun), whereas "PL("knifes")" will return "knife" ("knifes" having been treated as a 3rd person singular verb).

The inherent ambiguity of such cases suggests that, where the part of speech is known, "PL_N", "PL_V", and "PL_ADJ" should be used in preference to "PL".

Note that all these subroutines ignore any whitespace surrounding the word being inflected, but preserve that whitespace when the result is returned. For example, "PL(" cat  ")" returns " cats  ".

Numbered plurals

The "PL_..." subroutines return only the inflected word, not the count that was used to inflect it. Thus, in order to produce "I saw 3 ducks", it is necessary to use:

    print "I saw $N ", PL_N($animal,$N), "\n";

Since the usual purpose of producing a plural is to make it agree with a preceding count, Lingua::EN::Inflect provides an exportable subroutine ("NO($;$)") which, given a word and a(n optional) count, returns the count followed by the correctly inflected word. Hence the previous example can be rewritten:

    print "I saw ", NO($animal,$N), "\n";

In addition, if the count is zero (or some other term which implies zero, such as "zero", "nil", etc.) the count is replaced by the word "no". Hence, if $N had the value zero, the previous example would print the somewhat more elegant:

    I saw no animals

rather than:

    I saw 0 animals

Note that the name of the subroutine is a pun: the subroutine returns either a number (a No.) or a "no", in front of the inflected word.

Wordy and comma'd plurals

The "NO()" subroutine takes an optional third argument: a hash of named options that configure its behaviour.

The 'words_below' option informs "NO()" what other numbers (i.e. apart from zero) it should convert to words. For example:S

    for my $count (0..12) {
        print NO('cat', $count, {words_below => 10}), "\n";
    }

would print:

    no cats
    one cat
    two cats
    three cats
    four cats
    five cats
    six cats
    seven cats
    eight cats
    nine cats
    10 cats
    11 cats
    12 cats

The 'comma' and 'comma_every' options determine whether or not the numbers produced by "NO()" have commas in them. That is:

    2001 space odysseys

versus:

    2,001 space odysseys

Normally, numbers are produced without commas, but if 'comma' or 'comma_every' is specified, then commas are added as requested.

The 'comma' option specifies which character to use as a comma. It defaults to ',', but may be set to anything convenient:

    print NO('Euro', $amount, {comma=>'.'});
    # prints:  1.000.000 Euros

The 'comma_every' option specifies how many characters between commas. It defaults to 3, but may be set to any positive number:

    print NO('Euro', $amount, {comma_every=>4});
    # prints:  100,0000 Euros

Note that you can set both options at once, if you wish:

    print NO('Euro', $amount, {comma_every=>2, comma=>'_'});
    # prints:  1_00_00_00 Euros

Reducing the number of counts required

In some contexts, the need to supply an explicit count to the various "PL_..." subroutines makes for tiresome repetition. For example:

    print PL_ADJ("This",$errors), PL_N(" error",$errors),
          PL_V(" was",$errors), " fatal.\n";

Lingua::EN::Inflect therefore provides an exportable subroutine ("NUM($;$)") that may be used to set a persistent "default number" value. If such a value is set, it is subsequently used whenever an optional second "number" argument is omitted. The default value thus set can subsequently be removed by calling "NUM()" with no arguments. Hence we could rewrite the previous example:

    NUM($errors);
    print PL_ADJ("This"), PL_N(" error"), PL_V(" was"), "fatal.\n";
    NUM();

Normally, "NUM()" returns its first argument, so that it may also be "inlined" in contexts like:

    print NUM($errors), PL_N(" error"), PL_V(" was"), " detected.\n"
    print PL_ADJ("This"), PL_N(" error"), PL_V(" was"), "fatal.\n"
        if $severity > 1;

However, in certain contexts (see "INTERPOLATING INFLECTIONS IN STRINGS") it is preferable that "NUM()" return an empty string. Hence "NUM()" provides an optional second argument. If that argument is supplied (that is, if it is defined) and evaluates to false, "NUM" returns an empty string instead of its first argument. For example:

    print NUM($errors,0), NO("error"), PL_V(" was"), " detected.\n";
    print PL_ADJ("This"), PL_N(" error"), PL_V(" was"), "fatal.\n"
        if $severity > 1;

Number-insensitive equality

Lingua::EN::Inflect also provides a solution to the problem of comparing words of differing plurality through the exportable subroutines "PL_eq($$)", "PL_N_eq($$)", "PL_V_eq($$)", and "PL_ADJ_eq($$)". Each of these subroutines takes two strings, and compares them using the corresponding plural-inflection subroutine ("PL()", "PL_N()", "PL_V()", and "PL_ADJ()" respectively).

The comparison returns true if:

• the strings are "eq"-equal, or
• one string is "eq"-equal to a plural form of the other, or
• the strings are two different plural forms of the one word.

Hence all of the following return true:

    PL_eq("index","index")      # RETURNS "eq"
    PL_eq("index","indexes")    # RETURNS "s:p"
    PL_eq("index","indices")    # RETURNS "s:p"
    PL_eq("indexes","index")    # RETURNS "p:s"
    PL_eq("indices","index")    # RETURNS "p:s"
    PL_eq("indices","indexes")  # RETURNS "p:p"
    PL_eq("indexes","indices")  # RETURNS "p:p"
    PL_eq("indices","indices")  # RETURNS "eq"

As indicated by the comments in the previous example, the actual value returned by the various "PL_eq" subroutines encodes which of the three equality rules succeeded: "eq" is returned if the strings were identical, "s:p" if the strings were singular and plural respectively, "p:s" for plural and singular, and "p:p" for two distinct plurals. Inequality is indicated by returning an empty string.

It should be noted that two distinct singular words which happen to take the same plural form are not considered equal, nor are cases where one (singular) word's plural is the other (plural) word's singular. Hence all of the following return false:

    PL_eq("base","basis")       # ALTHOUGH BOTH -> "bases"
    PL_eq("syrinx","syringe")   # ALTHOUGH BOTH -> "syringes"
    PL_eq("she","he")       # ALTHOUGH BOTH -> "they"
    PL_eq("opus","operas")      # ALTHOUGH "opus" -> "opera" -> "operas"
    PL_eq("taxi","taxes")       # ALTHOUGH "taxi" -> "taxis" -> "taxes"

Note too that, although the comparison is "number-insensitive" it is not case-insensitive (that is, "PL("time","Times")" returns false. To obtain both number and case insensitivity, prefix both arguments with "lc" (that is, "PL(lc "time", lc "Times")" returns true).

Present participles

"Lingua::EN::Inflect" also provides the "PART_PRES" subroutine, which can take a 3rd person singular verb and correctly inflect it to its present participle:

    PART_PRES("runs")   # "running"
    PART_PRES("loves")  # "loving"
    PART_PRES("eats")   # "eating"
    PART_PRES("bats")   # "batting"
    PART_PRES("spies")  # "spying"

Selecting indefinite articles

Lingua::EN::Inflect provides two exportable subroutines ("A($;$)" and "AN($;$)") which will correctly prepend the appropriate indefinite article to a word, depending on its pronunciation. For example:

    A("cat")        # -> "a cat"
    AN("cat")       # -> "a cat"
    A("euphemism")      # -> "a euphemism"
    A("Euler number")   # -> "an Euler number"
    A("hour")       # -> "an hour"
    A("houri")      # -> "a houri"

The two subroutines are identical in function and may be used interchangeably. The only reason that two versions are provided is to enhance the readability of code such as:

    print "That is ", AN($errortype), " error\n;
    print "That is ", A($fataltype), " fatal error\n;

Note that in both cases the actual article provided depends only on the pronunciation of the first argument, not on the name of the subroutine.

"A()" and "AN()" will ignore any indefinite article that already exists at the start of the string. Thus:

    @half_arked = (
        "a elephant",
        "a giraffe",
        "an ewe",
        "a orangutan",
    );
    print A($_), "\n" for @half_arked;
    # prints:
    #     an elephant
    #     a giraffe
    #     a ewe
    #     an orangutan

"A()" and "AN()" both take an optional second argument. As with the "PL_..." subroutines, this second argument is a "number" specifier. If its value is 1 (or some other value implying singularity), "A()" and "AN()" insert "a" or "an" as appropriate. If the number specifier implies plurality, ("A()" and "AN()" insert the actual second argument instead. For example:

    A("cat",1)      # -> "a cat"
    A("cat",2)      # -> "2 cat"
    A("cat","one")      # -> "one cat"
    A("cat","no")       # -> "no cat"

Note that, as implied by the previous examples, "A()" and "AN()" both assume that their job is merely to provide the correct qualifier for a word (that is: "a", "an", or the specified count). In other words, they assume that the word they are given has already been correctly inflected for plurality. Hence, if $N has the value 2, then:

      print A("cat",$N);

prints "2 cat", instead of "2 cats". The correct approach is to use:

      print A(PL("cat",$N),$N);

or, better still:

      print NO("cat",$N);

Note too that, like the various "PL_..." subroutines, whenever "A()" and "AN()" are called with only one argument they are subject to the effects of any preceding call to "NUM()". Hence, another possible solution is:

      NUM($N);
      print A(PL("cat"));

Indefinite articles and initialisms

"Initialisms" (sometimes inaccurately called "acronyms") are terms which have been formed from the initial letters of words in a phrase (for example, "NATO", "NBL", "S.O.S.", "SCUBA", etc.)

Such terms present a particular challenge when selecting between "a" and "an", since they are sometimes pronounced as if they were a single word ("nay-tow", "sku-ba") and sometimes as a series of letter names ("en-eff-ell", "ess-oh-ess").

"A()" and "AN()" cope with this dichotomy using a series of inbuilt rules, which may be summarized as:

1.

If the word starts with a single letter, followed by a period or dash (for example, "R.I.P.", "C.O.D.", "e-mail", "X-ray", "T-square"), then choose the appropriate article for the sound of the first letter ("an R.I.P.", "a C.O.D.", "an e-mail", "an X-ray", "a T-square").

2.

If the first two letters of the word are capitals, consonants, and do not appear at the start of any known English word, (for example, "LCD", "XML", "YWCA"), then once again choose "a" or "an" depending on the sound of the first letter ("an LCD", "an XML", "a YWCA").

3.

Otherwise, assume the string is a capitalized word or a pronounceable initialism (for example, "LED", "OPEC", "FAQ", "UNESCO"), and therefore takes "a" or "an" according to the (apparent) pronunciation of the entire word ("a LED", "an OPEC", "a FAQ", "a UNESCO").

Note that rules 1 and 3 together imply that the presence or absence of punctuation may change the selection of indefinite article for a particular initialism (for example, "a FAQ" but "an F.A.Q.").

Indefinite articles and "soft H's"

Words beginning in the letter 'H' present another type of difficulty when selecting a suitable indefinite article. In a few such words (for example, "hour", "honour", "heir") the 'H' is not voiced at all, and so such words inflect with "an". The remaining cases ("voiced H's") may be divided into two categories: "hard H's" (such as "hangman", "holograph", "hat", etc.) and "soft H's" (such as "hysterical", "horrendous", "holy", etc.)

Hard H's always take "a" as their indefinite article, and soft H's normally do so as well. But some English speakers prefer "an" for soft H's (although the practice is now generally considered an affectation, rather than a legitimate grammatical alternative).

At present, the "A()" and "AN()" subroutines ignore soft H's and use "a" for any voiced 'H'. The author would, however, welcome feedback on this decision (envisaging a possible future "soft H" mode).

Adding plurals at run-time

Lingua::EN::Inflect provides five exportable subroutines which allow the programmer to override the module's behaviour for specific cases:

"def_noun($$)"

The "def_noun" subroutine takes a pair of string arguments: the singular and plural forms of the noun being specified. The singular form specifies a pattern to be interpolated (as "m/^(?:$first_arg)$/i"). Any noun matching this pattern is then replaced by the string in the second argument. The second argument specifies a string which is interpolated after the match succeeds, and is then used as the plural form. For example:

      def_noun  'cow'        => 'kine';
      def_noun  '(.+i)o'     => '$1i';
      def_noun  'spam(mer)?' => '\\$\\%\\@#\\$\\@#!!';
    

Note that both arguments should usually be specified in single quotes, so that they are not interpolated when they are specified, but later (when words are compared to them). As indicated by the last example, care also needs to be taken with certain characters in the second argument, to ensure that they are not unintentionally interpolated during comparison.

The second argument string may also specify a second variant of the plural form, to be used when "classical" plurals have been requested. The beginning of the second variant is marked by a '|' character:

      def_noun  'cow'        => 'cows|kine';
      def_noun  '(.+i)o'     => '$1os|$1i';
      def_noun  'spam(mer)?' => '\\$\\%\\@#\\$\\@#!!|varmints';
    

If no classical variant is given, the specified plural form is used in both normal and "classical" modes.

If the second argument is "undef" instead of a string, then the current user definition for the first argument is removed, and the standard plural inflection(s) restored.

Note that in all cases, later plural definitions for a particular singular form replace earlier definitions of the same form. For example:

      # FIRST, HIDE THE MODERN FORM....
      def_noun  'aviatrix' => 'aviatrices';
      # LATER, HIDE THE CLASSICAL FORM...
      def_noun  'aviatrix' => 'aviatrixes';
      # FINALLY, RESTORE THE DEFAULT BEHAVIOUR...
      def_noun  'aviatrix' => undef;
    

Special care is also required when defining general patterns and associated specific exceptions: put the more specific cases after the general pattern. For example:

      def_noun  '(.+)us' => '$1i';      # EVERY "-us" TO "-i"
      def_noun  'bus'    => 'buses';    # EXCEPT FOR "bus"
    

This "try-most-recently-defined-first" approach to matching user-defined words is also used by "def_verb", "def_a" and "def_an".

"def_verb($$$$$$)"

The "def_verb" subroutine takes three pairs of string arguments (that is, six arguments in total), specifying the singular and plural forms of the three "persons" of verb. As with "def_noun", the singular forms are specifications of run-time-interpolated patterns, whilst the plural forms are specifications of (up to two) run-time-interpolated strings:

       def_verb 'am'       => 'are',
                'are'      => 'are|art',
                'is'       => 'are';
       def_verb 'have'     => 'have',
                'have'     => 'have',
                'ha(s|th)' => 'have';
    

Note that as with "def_noun", modern/classical variants of plurals may be separately specified, subsequent definitions replace previous ones, and "undef"'ed plural forms revert to the standard behaviour.

"def_adj($$)"

The "def_adj" subroutine takes a pair of string arguments, which specify the singular and plural forms of the adjective being defined. As with "def_noun" and "def_adj", the singular forms are specifications of run-time-interpolated patterns, whilst the plural forms are specifications of (up to two) run-time-interpolated strings:

       def_adj  'this'     => 'these',
       def_adj  'red'      => 'red|gules',
    

As previously, modern/classical variants of plurals may be separately specified, subsequent definitions replace previous ones, and "undef"'ed plural forms revert to the standard behaviour.

def_a($) and def_an($)

The "def_a" and "def_an" subroutines each take a single argument, which specifies a pattern. If a word passed to "A()" or "AN()" matches this pattern, it will be prefixed (unconditionally) with the corresponding indefinite article. For example:

      def_a  'error';
      def_a  'in.+';
      def_an 'mistake';
      def_an 'error';
    

As with the other "def_..." subroutines, such redefinitions are sequential in effect so that, after the above example, "error" will be inflected with "an".

The $HOME/.inflectrc file

When it is imported, Lingua::EN::Inflect executes (as Perl code) the contents of any file named .inflectrc which it finds in the in the directory where Lingua/EN/Inflect.pm is installed, or in the current home directory ($ENV{HOME}), or in both. Note that the code is executed within the Lingua::EN::Inflect namespace.

Hence the user or the local Perl guru can make appropriate calls to "def_noun", "def_verb", etc. in one of these .inflectrc files, to permanently and universally modify the behaviour of the module. For example

      > cat /usr/local/lib/perl5/Text/Inflect/.inflectrc
      def_noun  "UNIX"  => "UN*X|UNICES";
      def_verb  "teco"  => "teco",      # LITERALLY: "to edit with TECO"
                "teco"  => "teco",
                "tecos" => "teco";
      def_a     "Euler.*";              # "Yewler" TURNS IN HIS GRAVE

Note that calls to the "def_..." subroutines from within a program will take precedence over the contents of the home directory .inflectrc file, which in turn takes precedence over the system-wide .inflectrc file.

2nd Person precedence

If a verb has identical 1st and 2nd person singular forms, but different 1st and 2nd person plural forms, then when its plural is constructed, the 2nd person plural form is always preferred.

The author is not currently aware of any such verbs in English, but is not quite arrogant enough to assume ipso facto that none exist.

Nominative precedence

The singular pronoun "it" presents a special problem because its plural form can vary, depending on its "case". For example:

        It ate my homework       ->  They ate my homework
        It ate it                ->  They ate them
        I fed my homework to it  ->  I fed my homework to them

As a consequence of this ambiguity, "PL()" or "PL_N" have been implemented so that they always return the nominative plural (that is, "they").

However, when asked for the plural of an unambiguously accusative "it" (namely, "PL("to it")", "PL_N("from it")", "PL("with it")", etc.), both subroutines will correctly return the accusative plural ("to them", "from them", "with them", etc.)

The plurality of zero

The rules governing the choice between:

      There were no errors.

and

      There was no error.

are complex and often depend more on intent rather than content. Hence it is infeasible to specify such rules algorithmically.

Therefore, Lingua::EN::Text contents itself with the following compromise: If the governing number is zero, inflections always return the plural form unless the appropriate "classical" inflection is in effect, in which case the singular form is always returned.

Thus, the sequence:

      NUM(0);
      print inflect "There PL(was) NO(choice)";

produces "There were no choices", whereas:

      classical 'zero';     # or: classical(zero=>1);
      NUM(0);
      print inflect "There PL(was) NO(choice)";

it will print "There was no choice".

Homographs with heterogeneous plurals

Another context in which intent (and not content) sometimes determines plurality is where two distinct meanings of a word require different plurals. For example:

      Three basses were stolen from the band's equipment trailer.
      Three bass were stolen from the band's aquarium.
      I put the mice next to the cheese.
      I put the mouses next to the computers.
      Several thoughts about leaving crossed my mind.
      Several thought about leaving across my lawn.

Lingua::EN::Inflect handles such words in two ways:

• If both meanings of the word are the same part of speech (for example, "bass" is a noun in both sentences above), then one meaning is chosen as the "usual" meaning, and only that meaning's plural is ever returned by any of the inflection subroutines.
• If each meaning of the word is a different part of speech (for example, "thought" is both a noun and a verb), then the noun's plural is returned by "PL()" and "PL_N()" and the verb's plural is returned only by "PL_V()".

Such contexts are, fortunately, uncommon (particularly "same-part-of-speech" examples). An informal study of nearly 600 "difficult plurals" indicates that "PL()" can be relied upon to "get it right" about 98% of the time (although, of course, ichthyophilic guitarists or cyber-behaviouralists may experience higher rates of confusion).

If the choice of a particular "usual inflection" is considered inappropriate, it can always be reversed with a preliminary call to the corresponding "def_..." subroutine.