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Inflects English nouns and verbs.

Strings::Inflection provides English inflections of nouns and verbs component for Strings.


The goal is to provide a comprehensive way to inflect most nouns and verbs in English. The algorithms that this gem uses are based on the analysis of 7,000 most frequently used nouns and 6,000 most used verbs in English language. Because of this you will get correct inflections for most words:

Strings::Inflection.pluralize("cod") # => "cod"
Strings::Inflection.pluralize("codex") # => "codices"
Strings::Inflection.pluralize("criterion") # => "criteria"
Strings::Inflection.pluralize("vertebra") # => "vertebrae"


Add this line to your application's Gemfile:

gem 'strings-inflection'

And then execute:

$ bundle

Or install it yourself as:

$ gem install strings-inflection


1. Usage

Strings::Inflection provides a generic inflect method for transforming noun or verb inflections. In the most common case, it assumes that you wish to transform a noun to another form based on count:

Strings::Inflection.inflect("error", 3)
# => "errors"

As a shortcut, when you wish to always convert a word to singular form use singularize or pluralize for the opposite:

Strings::Inflection.singularize("errors") # => "error"
Strings::Inflection.pluralize("error") # => "errors"
Strings::Inflection.singularize("try", term: :verb) # => "tries"
Strings::Inflection.pluralize("tries", term: :verb) # => "try"

Alternatively, you can convert words into a noun or verb object. This way you gain access to singularand plural methods:

Strings::Inflection::Noun("errors").singular # => "error"
Strings::Inflection::Noun("error").plural # => "errors"
Strings::Inflection::Verb("try").singular # => "tries"
Strings::Inflection::Verb("tries").plural # => "try"

The inflect method also accepts a mustache-like template to inflect more complex phrases and sentences:

Strings::Inflection.inflect("{{#:count}} {{N:error}} {{V:was}} found", 3)
# => "3 errors were found"

To change any inflection rules, you can change them using configure. By default the rules only apply to nouns.

Strings::Inflection.configure do |config|
  config.plural "index", "indexes"
  config.singular "axes", "ax"

Then the inflection will behave like this:

Strings::Inflection.pluralize("index") # => "indexes"
Strings::Inflection.singularize("axes") # => "ax"

2. API

2.1 inflect

In the most common case, to change a noun's inflection use inflect method with the word and a count. By default inflect assumes a noun.

For example, to inflect the noun error to its plural form do:

Strings::Inflection.inflect("error", 2) # => "errors"

And to inflect a verb, use the :term option:

Strings::Inflection.inflect("tries", 2, term: :verb) # => "try"

For more complex cases when you want to inflect parts of a sentence, the inflect provides tags in a template.

For example, you can inflect a noun and a verb to display information based on the count:

Strings::Inflection.inflect("{{#:count}} {{N:error}} {{V:was}} found", 2)
# => "2 errors were found"

2.1.1 template

The template inflects any content inside mustache-like braces {{...}}. The general form of content inside tag is {{Xmod:word}} where:

  • X informs a grammatical function to apply to word out of N or V and #.
  • mod apply zero or more modifiers to word transformation.
  • word represents the string to inflect.

The available tags are:

{{#: count }}

The first type of tag is the count tag. By default, this tag will display the count inside the evaluated string.

String::Inflection.inflect("{{#:count}} found", 2)
# => "2 found"

There is an f option that will provide a fuzzy estimation of the count:

String::Inflection.inflect("{{#f:count}}", 0) # => "no"
String::Inflection.inflect("{{#f:count}}", 1) # => "one"
String::Inflection.inflect("{{#f:count}}", 2) # => "a couple of"
String::Inflection.inflect("{{#f:count}}", 3) # => "a few"
String::Inflection.inflect("{{#f:count}}", 6) # => "several"
String::Inflection.inflect("{{#f:count}}", 12) # => "many"

{{N: word }}

This tag inflects a noun into a singular or plural form based on the provided count.

Strings::Inflection.inflect("{{#:count}} {{N:error}} found", 3)
# => "3 errors found"

You can supply s or p options to always force a noun to be singular or plural form.

Strings::Inflection.inflect("{{#:count}} {{Ns:error}} found", 3)
# => "3 error found"

{{V: word }}

This tag inflects a verb into appropriate form based on the provided count.

Strings::Inflection.inflect("There {{V:were}} {{#:count}} {{N:match}} found", 1)
# => "There was 1 match found"

2.2 singularize

You can transform a noun or a verb into singular form with singularize method. By default it assumes a noun but you can change this with :term option:

Strings::Inflection.singularize("errors") # => "error"
Strings::Inflection.singularize("indices") # => "index"
Strings::Inflection.singularize("index", term: :verb) # => "indexes"
Strings::Inflection.singularize("try", term: :verb) # => "tries"

It will handle inflecting irregular nouns or verbs as well:

Strings::Inflection.singularize("feet") # => "foot"
Strings::Inflection.singularize("are", term: :verb) # => "is"
Strings::Inflection.singularize("go", term: :verb) # => "goes"

This method won't change inflection if it already is in the correct form:

Strings::Inflection.singularize("index") # => "index"
Strings::Inflection.singularize("sees") # => "sees"

2.3 singular?

To check if a noun or a verb is in a singular form use singular?:

Strings::Inflection.singular?("errors") # => false
Strings::Inflection.singular?("index") # => true
Strings::Inflection.singular?("try", term: :verb) # => false
Strings::Inflection.singular?("goes", term: :verb) # => true

You can also convert a word to a noun or verb object:

Strings::Inflection::Noun("errors").singular? # => false
Strings::Inflection::Noun("index").singular? # => true
Strings::Inflection::Verb("try").singular? # => false
Strings::Inflection::Verb("goes").singular? # => true

2.4 pluralize

You can transform a noun or a verb into plural form with pluralize method. By default it assumes a noun but you can change this with :term option:

Strings::Inflection.pluralize("error") # => "errors"
Strings::Inflection.pluralize("index") # => "indices"
Strings::Inflection.pluralize("indexes", term: :verb) # => "index"
Strings::Inflection.pluralize("tries", term: :verb) # => "try"

It will handle inflecting irregular nouns or verbs as well:

Strings::Inflection.pluralize("foot") # => "feet"
Strings::Inflection.pluralize("is", term: :verb) # => "are"
Strings::Inflection.pluralize("goes", term: :verb) # => "go"

This method won't change inflection if it already is in the correct form:

Strings::Inflection.pluralize("indices") # => "indices"
Strings::Inflection.pluralize("go") # => "go"

2.5 plural?

To check if a noun or a verb is in a plural form use plural?:

Strings::Inflection.plural?("errors") # => true
Strings::Inflection.plural?("index") # => false
Strings::Inflection.plural?("try", term: :verb) # => true
Strings::Inflection.plural?("goes", term: :verb) # => false

You can also convert a word to a noun or verb object:

Strings::Inflection::Noun("errors").plural? # => true
Strings::Inflection::Noun("index").plural? # => false
Strings::Inflection::Verb("try").plural? # => true
Strings::Inflection::Verb("goes").plural? # => false

2.6 join_words

To join an array of words into a single sentence use join_words method.

For example, to join three words:

Strings::Inflection.join_words("one", "two", "three")
# => "one, two, and three"

To join words without Oxford style comma use :final_separator:

Strings::Inflection.join_words("one", "two", "three", final_separator: "")
# => "one, two and three"

To join words with custom separators:

options = {
  separator: " or ",
  final_separator: " or at least ",
  conjunctive: ""
Strings::Inflection.join_words("one", "two", "three", **options)
# => "one or two or at least three"

You can also use noun objects to join words. We could do the above:

N = Strings::Inflection::Noun
(N("one") + "two" + "three").join_words
# => "one, two, and three"

2.7 configure

To change any inflection rules use configure with a block. By default the rules only apply to nouns.

Inside the block, the configuration exposes few methods:

  • plural - add plural form inflection rule
  • singular - add singular form inflection rule
  • rule - add singular and plural form inflection rule
  • uncountable - add uncountable nouns

For example, to add new plural and singular rules for the index and ax nouns do:

Strings::Inflection.configure do |config|
  config.plural "index", "indexes"
  config.singular "axes", "ax"

To add a rule for both singular and plural inflections do:

Strings::Inflection.configure do |config|
  config.rule "ax", "axes"

To add an uncountable noun do:

Strings::Inflection.configure do |config|
  config.uncountable "east", "earnings"

Now, no inflection will be applied:

Strings::Inflection.inflect("earnings", 1) # => "earnings"
Strings::Inflection.inflect("east", 2) # => "east"

3. Extending String class

Though it is highly discouraged to pollute core Ruby classes, you can add the required methods to String class by using refinements.

For example, if you wish to only extend strings with inflect method do:

module MyStringExt
  refine String do
    def inflect(*args, **options)
      Strings::Inflection.inflect(self, *args, **options)

Then inflect method will be available for any strings where refinement is applied:

using MyStringExt

"error".inflect(2) # => "errors"
"are".inflect(1, term: :verb) # => "is"

However, if you want to include all the Strings::Inflection methods, you can use provided extensions file:

require "strings/inflection/extensions"

using Strings::Inflection::Extensions


After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to


Bug reports and pull requests are welcome on GitHub at This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.


The gem is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the Strings::Inflection project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.


Copyright (c) 2019 Piotr Murach. See LICENSE for further details.


Convert between singular and plural forms of English nouns




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