diff --git a/actionpack/lib/action_controller/metal/mime_responds.rb b/actionpack/lib/action_controller/metal/mime_responds.rb
index 6469e24d361fc..9885110d5dd48 100644
--- a/actionpack/lib/action_controller/metal/mime_responds.rb
+++ b/actionpack/lib/action_controller/metal/mime_responds.rb
@@ -1,5 +1,6 @@
 require 'abstract_controller/collector'
 require 'active_support/core_ext/class/attribute'
+require 'active_support/core_ext/object/inclusion'
 
 module ActionController #:nodoc:
   module MimeResponds #:nodoc:
@@ -248,9 +249,9 @@ def collect_mimes_from_class_level #:nodoc:
         config = self.class.mimes_for_respond_to[mime]
 
         if config[:except]
-          !config[:except].include?(action)
+          !action.in?(config[:except])
         elsif config[:only]
-          config[:only].include?(action)
+          action.in?(config[:only])
         else
           true
         end
diff --git a/actionpack/lib/action_dispatch/routing/mapper.rb b/actionpack/lib/action_dispatch/routing/mapper.rb
index 35be0b3a27982..d054028bc3558 100644
--- a/actionpack/lib/action_dispatch/routing/mapper.rb
+++ b/actionpack/lib/action_dispatch/routing/mapper.rb
@@ -1,6 +1,7 @@
 require 'erb'
 require 'active_support/core_ext/hash/except'
 require 'active_support/core_ext/object/blank'
+require 'active_support/core_ext/object/inclusion'
 require 'active_support/inflector'
 require 'action_dispatch/routing/redirection'
 
@@ -1345,11 +1346,11 @@ def scope_action_options #:nodoc:
           end
 
           def resource_scope? #:nodoc:
-            [:resource, :resources].include?(@scope[:scope_level])
+            @scope[:scope_level].either?(:resource, :resources)
           end
 
           def resource_method_scope? #:nodoc:
-            [:collection, :member, :new].include?(@scope[:scope_level])
+            @scope[:scope_level].either?(:collection, :member, :new)
           end
 
           def with_exclusive_scope
diff --git a/actionpack/lib/action_dispatch/testing/assertions/response.rb b/actionpack/lib/action_dispatch/testing/assertions/response.rb
index 77a15f3e97943..d3e7fa388f999 100644
--- a/actionpack/lib/action_dispatch/testing/assertions/response.rb
+++ b/actionpack/lib/action_dispatch/testing/assertions/response.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/object/inclusion'
+
 module ActionDispatch
   module Assertions
     # A small suite of assertions that test responses from \Rails applications.
@@ -33,7 +35,7 @@ module ResponseAssertions
       def assert_response(type, message = nil)
         validate_request!
 
-        if [ :success, :missing, :redirect, :error ].include?(type) && @response.send("#{type}?")
+        if type.either?(:success, :missing, :redirect, :error) && @response.send("#{type}?")
           assert_block("") { true } # to count the assertion
         elsif type.is_a?(Fixnum) && @response.response_code == type
           assert_block("") { true } # to count the assertion
diff --git a/actionpack/lib/action_dispatch/testing/assertions/selector.rb b/actionpack/lib/action_dispatch/testing/assertions/selector.rb
index 2b862fb7d68ed..3346fa2a04c98 100644
--- a/actionpack/lib/action_dispatch/testing/assertions/selector.rb
+++ b/actionpack/lib/action_dispatch/testing/assertions/selector.rb
@@ -1,4 +1,5 @@
 require 'action_controller/vendor/html-scanner'
+require 'active_support/core_ext/object/inclusion'
 
 #--
 # Copyright (c) 2006 Assaf Arkin (http://labnotes.org)
@@ -441,7 +442,7 @@ def assert_select_rjs(*args, &block)
 
         if matches
           assert_block("") { true } # to count the assertion
-          if block_given? && !([:remove, :show, :hide, :toggle].include? rjs_type)
+          if block_given? && !rjs_type.either?(:remove, :show, :hide, :toggle)
             begin
               @selected ||= nil
               in_scope, @selected = @selected, matches
diff --git a/actionpack/lib/action_dispatch/testing/integration.rb b/actionpack/lib/action_dispatch/testing/integration.rb
index 9b2f534457a25..a5080203685a0 100644
--- a/actionpack/lib/action_dispatch/testing/integration.rb
+++ b/actionpack/lib/action_dispatch/testing/integration.rb
@@ -1,6 +1,7 @@
 require 'stringio'
 require 'uri'
 require 'active_support/core_ext/kernel/singleton_class'
+require 'active_support/core_ext/object/inclusion'
 require 'active_support/core_ext/object/try'
 require 'rack/test'
 require 'test/unit/assertions'
@@ -320,7 +321,7 @@ def reset!
         define_method(method) do |*args|
           reset! unless integration_session
           # reset the html_document variable, but only for new get/post calls
-          @html_document = nil unless %w(cookies assigns).include?(method)
+          @html_document = nil unless method.either?("cookies", "assigns")
           integration_session.__send__(method, *args).tap do
             copy_session_variables!
           end
diff --git a/actionpack/test/controller/mime_responds_test.rb b/actionpack/test/controller/mime_responds_test.rb
index 41f80d0784875..6c5dc09011deb 100644
--- a/actionpack/test/controller/mime_responds_test.rb
+++ b/actionpack/test/controller/mime_responds_test.rb
@@ -1,6 +1,7 @@
 require 'abstract_unit'
 require 'controller/fake_models'
 require 'active_support/core_ext/hash/conversions'
+require 'active_support/core_ext/object/inclusion'
 
 class StarStarMimeController < ActionController::Base
   layout nil
@@ -158,7 +159,7 @@ def rescue_action(e)
 
   protected
     def set_layout
-      if ["all_types_with_layout", "iphone_with_html_response_type"].include?(action_name)
+      if action_name.either?("all_types_with_layout", "iphone_with_html_response_type")
         "respond_to/layouts/standard"
       elsif action_name == "iphone_with_html_response_type_without_layout"
         "respond_to/layouts/missing"
diff --git a/actionpack/test/controller/resources_test.rb b/actionpack/test/controller/resources_test.rb
index acb4617a60863..6ea492cf8b614 100644
--- a/actionpack/test/controller/resources_test.rb
+++ b/actionpack/test/controller/resources_test.rb
@@ -1,6 +1,7 @@
 require 'abstract_unit'
 require 'active_support/core_ext/object/try'
 require 'active_support/core_ext/object/with_options'
+require 'active_support/core_ext/object/inclusion'
 
 class ResourcesController < ActionController::Base
   def index() render :nothing => true end
@@ -1292,7 +1293,7 @@ def assert_named_route(expected, route, options)
     def assert_resource_methods(expected, resource, action_method, method)
       assert_equal expected.length, resource.send("#{action_method}_methods")[method].size, "#{resource.send("#{action_method}_methods")[method].inspect}"
       expected.each do |action|
-        assert resource.send("#{action_method}_methods")[method].include?(action),
+        assert action.in?(resource.send("#{action_method}_methods")[method])
           "#{method} not in #{action_method} methods: #{resource.send("#{action_method}_methods")[method].inspect}"
       end
     end
@@ -1329,9 +1330,9 @@ def assert_whether_allowed(allowed, not_allowed, options, action, path, method)
       options = options.merge(:action => action.to_s)
       path_options = { :path => path, :method => method }
 
-      if Array(allowed).include?(action)
+      if action.in?(Array(allowed))
         assert_recognizes options, path_options
-      elsif Array(not_allowed).include?(action)
+      elsif action.in?(Array(not_allowed))
         assert_not_recognizes options, path_options
       end
     end
diff --git a/actionpack/test/dispatch/routing_test.rb b/actionpack/test/dispatch/routing_test.rb
index 5e5758a60e7c0..51355b3ac7561 100644
--- a/actionpack/test/dispatch/routing_test.rb
+++ b/actionpack/test/dispatch/routing_test.rb
@@ -1,6 +1,7 @@
 require 'erb'
 require 'abstract_unit'
 require 'controller/fake_controllers'
+require 'active_support/core_ext/object/inclusion'
 
 class TestRoutingMapper < ActionDispatch::IntegrationTest
   SprocketsApp = lambda { |env|
@@ -495,7 +496,7 @@ def self.call(params, request)
         resources :todos, :id => /\d+/
       end
 
-      scope '/countries/:country', :constraints => lambda { |params, req| %[all France].include?(params[:country]) } do
+      scope '/countries/:country', :constraints => lambda { |params, req| params[:country].either?("all", "france") } do
         match '/',       :to => 'countries#index'
         match '/cities', :to => 'countries#cities'
       end
diff --git a/actionpack/test/template/erb_util_test.rb b/actionpack/test/template/erb_util_test.rb
index d1891094e860f..30f6d1a213504 100644
--- a/actionpack/test/template/erb_util_test.rb
+++ b/actionpack/test/template/erb_util_test.rb
@@ -1,4 +1,5 @@
 require 'abstract_unit'
+require 'active_support/core_ext/object/inclusion'
 
 class ErbUtilTest < Test::Unit::TestCase
   include ERB::Util
@@ -29,7 +30,7 @@ def test_html_escape_passes_html_escpe_unmodified
 
   def test_rest_in_ascii
     (0..127).to_a.map {|int| int.chr }.each do |chr|
-      next if %w(& " < >).include?(chr)
+      next if chr.in?('&"<>')
       assert_equal chr, html_escape(chr)
     end
   end
diff --git a/actionpack/test/template/form_helper_test.rb b/actionpack/test/template/form_helper_test.rb
index ff183d097d994..fa0709179bcf2 100644
--- a/actionpack/test/template/form_helper_test.rb
+++ b/actionpack/test/template/form_helper_test.rb
@@ -1,5 +1,6 @@
 require 'abstract_unit'
 require 'controller/fake_models'
+require 'active_support/core_ext/object/inclusion'
 
 class FormHelperTest < ActionView::TestCase
   tests ActionView::Helpers::FormHelper
@@ -1743,7 +1744,7 @@ def test_form_for_with_labelled_builder
   def snowman(method = nil)
     txt =  %{<div style="margin:0;padding:0;display:inline">}
     txt << %{<input name="utf8" type="hidden" value="&#x2713;" />}
-    if (method && !['get','post'].include?(method.to_s))
+    if method && !method.to_s.either?('get', 'post')
       txt << %{<input name="_method" type="hidden" value="#{method}" />}
     end
     txt << %{</div>}
diff --git a/actionpack/test/template/form_options_helper_test.rb b/actionpack/test/template/form_options_helper_test.rb
index 93ff7ba0fd4ec..6112bb7b2028e 100644
--- a/actionpack/test/template/form_options_helper_test.rb
+++ b/actionpack/test/template/form_options_helper_test.rb
@@ -1,5 +1,6 @@
 require 'abstract_unit'
 require 'tzinfo'
+require 'active_support/core_ext/object/inclusion'
 
 class Map < Hash
   def category
@@ -82,7 +83,7 @@ def test_collection_options_with_preselected_and_disabled_value
   def test_collection_options_with_proc_for_disabled
     assert_dom_equal(
       "<option value=\"&lt;Abe&gt;\">&lt;Abe&gt; went home</option>\n<option value=\"Babe\" disabled=\"disabled\">Babe went home</option>\n<option value=\"Cabe\" disabled=\"disabled\">Cabe went home</option>",
-      options_from_collection_for_select(dummy_posts, "author_name", "title", :disabled => lambda{|p| %w(Babe Cabe).include? p.author_name })
+      options_from_collection_for_select(dummy_posts, "author_name", "title", :disabled => lambda{|p| p.author_name.either?("Babe", "Cabe") })
     )
   end
 
diff --git a/actionpack/test/template/form_tag_helper_test.rb b/actionpack/test/template/form_tag_helper_test.rb
index f8671f298088d..2d6e71d39a34c 100644
--- a/actionpack/test/template/form_tag_helper_test.rb
+++ b/actionpack/test/template/form_tag_helper_test.rb
@@ -1,4 +1,5 @@
 require 'abstract_unit'
+require 'active_support/core_ext/object/inclusion'
 
 class FormTagHelperTest < ActionView::TestCase
   tests ActionView::Helpers::FormTagHelper
@@ -13,7 +14,7 @@ def snowman(options = {})
 
     txt =  %{<div style="margin:0;padding:0;display:inline">}
     txt << %{<input name="utf8" type="hidden" value="&#x2713;" />}
-    if (method && !['get','post'].include?(method.to_s))
+    if method && !method.to_s.either?('get','post')
       txt << %{<input name="_method" type="hidden" value="#{method}" />}
     end
     txt << %{</div>}
diff --git a/activemodel/lib/active_model/validator.rb b/activemodel/lib/active_model/validator.rb
index c5ed8d22d33e6..64fe99b62ddd0 100644
--- a/activemodel/lib/active_model/validator.rb
+++ b/activemodel/lib/active_model/validator.rb
@@ -1,6 +1,7 @@
 require 'active_support/core_ext/array/wrap'
 require "active_support/core_ext/module/anonymous"
 require 'active_support/core_ext/object/blank'
+require 'active_support/core_ext/object/inclusion'
 
 module ActiveModel #:nodoc:
 
@@ -67,7 +68,7 @@ module ActiveModel #:nodoc:
   #
   #   class TitleValidator < ActiveModel::EachValidator
   #     def validate_each(record, attribute, value)
-  #       record.errors[attribute] << 'must be Mr. Mrs. or Dr.' unless ['Mr.', 'Mrs.', 'Dr.'].include?(value)
+  #       record.errors[attribute] << 'must be Mr. Mrs. or Dr.' unless value.either?('Mr.', 'Mrs.', 'Dr.')
   #     end
   #   end
   #
diff --git a/activemodel/test/cases/mass_assignment_security/sanitizer_test.rb b/activemodel/test/cases/mass_assignment_security/sanitizer_test.rb
index 015153ec7cf67..9a73a5ad915e9 100644
--- a/activemodel/test/cases/mass_assignment_security/sanitizer_test.rb
+++ b/activemodel/test/cases/mass_assignment_security/sanitizer_test.rb
@@ -1,5 +1,6 @@
 require "cases/helper"
 require 'logger'
+require 'active_support/core_ext/object/inclusion'
 
 class SanitizerTest < ActiveModel::TestCase
 
@@ -9,7 +10,7 @@ class SanitizingAuthorizer
     attr_accessor :logger
 
     def deny?(key)
-       [ 'admin' ].include?(key)
+      key.in?(['admin'])
     end
 
   end
diff --git a/activerecord/lib/active_record/associations/association.rb b/activerecord/lib/active_record/associations/association.rb
index 27c446b12c30d..b250783d9e659 100644
--- a/activerecord/lib/active_record/associations/association.rb
+++ b/activerecord/lib/active_record/associations/association.rb
@@ -1,4 +1,5 @@
 require 'active_support/core_ext/array/wrap'
+require 'active_support/core_ext/object/inclusion'
 
 module ActiveRecord
   module Associations
@@ -163,7 +164,7 @@ def interpolate(sql, record = nil)
         def creation_attributes
           attributes = {}
 
-          if [:has_one, :has_many].include?(reflection.macro) && !options[:through]
+          if reflection.macro.either?(:has_one, :has_many) && !options[:through]
             attributes[reflection.foreign_key] = owner[reflection.active_record_primary_key]
 
             if reflection.options[:as]
diff --git a/activerecord/lib/active_record/associations/builder/belongs_to.rb b/activerecord/lib/active_record/associations/builder/belongs_to.rb
index 964e7fddc8d70..9ea37da78fbd9 100644
--- a/activerecord/lib/active_record/associations/builder/belongs_to.rb
+++ b/activerecord/lib/active_record/associations/builder/belongs_to.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/object/inclusion'
+
 module ActiveRecord::Associations::Builder
   class BelongsTo < SingularAssociation #:nodoc:
     self.macro = :belongs_to
@@ -65,7 +67,7 @@ def add_touch_callbacks(reflection)
 
       def configure_dependency
         if options[:dependent]
-          unless [:destroy, :delete].include?(options[:dependent])
+          unless options[:dependent].either?(:destroy, :delete)
             raise ArgumentError, "The :dependent option expects either :destroy or :delete (#{options[:dependent].inspect})"
           end
 
diff --git a/activerecord/lib/active_record/associations/builder/has_many.rb b/activerecord/lib/active_record/associations/builder/has_many.rb
index 77bb66228df4d..3b489d9647bf7 100644
--- a/activerecord/lib/active_record/associations/builder/has_many.rb
+++ b/activerecord/lib/active_record/associations/builder/has_many.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/object/inclusion'
+
 module ActiveRecord::Associations::Builder
   class HasMany < CollectionAssociation #:nodoc:
     self.macro = :has_many
@@ -14,7 +16,7 @@ def build
 
       def configure_dependency
         if options[:dependent]
-          unless [:destroy, :delete_all, :nullify, :restrict].include?(options[:dependent])
+          unless options[:dependent].either?(:destroy, :delete_all, :nullify, :restrict)
             raise ArgumentError, "The :dependent option expects either :destroy, :delete_all, " \
                                  ":nullify or :restrict (#{options[:dependent].inspect})"
           end
diff --git a/activerecord/lib/active_record/associations/builder/has_one.rb b/activerecord/lib/active_record/associations/builder/has_one.rb
index 07ba5d088efc7..7efe2ec74df4b 100644
--- a/activerecord/lib/active_record/associations/builder/has_one.rb
+++ b/activerecord/lib/active_record/associations/builder/has_one.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/object/inclusion'
+
 module ActiveRecord::Associations::Builder
   class HasOne < SingularAssociation #:nodoc:
     self.macro = :has_one
@@ -27,7 +29,7 @@ def validate_options
 
       def configure_dependency
         if options[:dependent]
-          unless [:destroy, :delete, :nullify, :restrict].include?(options[:dependent])
+          unless options[:dependent].either?(:destroy, :delete, :nullify, :restrict)
             raise ArgumentError, "The :dependent option expects either :destroy, :delete, " \
                                  ":nullify or :restrict (#{options[:dependent].inspect})"
           end
diff --git a/activerecord/lib/active_record/associations/has_one_association.rb b/activerecord/lib/active_record/associations/has_one_association.rb
index 1d2e8667e482a..82f5696ad8738 100644
--- a/activerecord/lib/active_record/associations/has_one_association.rb
+++ b/activerecord/lib/active_record/associations/has_one_association.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/object/inclusion'
+
 module ActiveRecord
   # = Active Record Belongs To Has One Association
   module Associations
@@ -50,7 +52,7 @@ def set_new_record(record)
         end
 
         def remove_target!(method)
-          if [:delete, :destroy].include?(method)
+          if method.either?(:delete, :destroy)
             target.send(method)
           else
             nullify_owner_attributes(target)
diff --git a/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb b/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
index 6aac96df6f740..032a3135f06b1 100644
--- a/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
+++ b/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
@@ -1,4 +1,5 @@
 require 'active_support/core_ext/class/attribute'
+require 'active_support/core_ext/object/inclusion'
 
 module ActiveRecord
   module AttributeMethods
@@ -58,7 +59,7 @@ def #{attr_name}=(original_time)
 
         private
           def create_time_zone_conversion_attribute?(name, column)
-            time_zone_aware_attributes && !self.skip_time_zone_conversion_for_attributes.include?(name.to_sym) && [:datetime, :timestamp].include?(column.type)
+            time_zone_aware_attributes && !self.skip_time_zone_conversion_for_attributes.include?(name.to_sym) && column.type.either?(:datetime, :timestamp)
           end
       end
     end
diff --git a/activerecord/lib/active_record/railties/databases.rake b/activerecord/lib/active_record/railties/databases.rake
index ff368146842b7..a1b0270d1b9fa 100644
--- a/activerecord/lib/active_record/railties/databases.rake
+++ b/activerecord/lib/active_record/railties/databases.rake
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/object/inclusion'
+
 db_namespace = namespace :db do
   task :load_config => :rails_env do
     require 'active_record'
@@ -135,7 +137,7 @@ db_namespace = namespace :db do
   end
 
   def local_database?(config, &block)
-    if %w( 127.0.0.1 localhost ).include?(config['host']) || config['host'].blank?
+    if config['host'].either?("127.0.0.1", "localhost") || config['host'].blank?
       yield
     else
       $stderr.puts "This task only modifies local databases. #{config['database']} is on a remote host."
diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index e801bc4afae54..82561e86cf525 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -1,5 +1,6 @@
 require 'active_support/core_ext/class/attribute'
 require 'active_support/core_ext/module/deprecation'
+require 'active_support/core_ext/object/inclusion'
 
 module ActiveRecord
   # = Active Record Reflection
@@ -163,7 +164,7 @@ def klass
 
       def initialize(macro, name, options, active_record)
         super
-        @collection = [:has_many, :has_and_belongs_to_many].include?(macro)
+        @collection = macro.either?(:has_many, :has_and_belongs_to_many)
       end
 
       # Returns a new, unsaved instance of the associated class. +options+ will
diff --git a/activerecord/lib/rails/generators/active_record/session_migration/session_migration_generator.rb b/activerecord/lib/rails/generators/active_record/session_migration/session_migration_generator.rb
index afcda2a98a494..e803ee5764f8a 100644
--- a/activerecord/lib/rails/generators/active_record/session_migration/session_migration_generator.rb
+++ b/activerecord/lib/rails/generators/active_record/session_migration/session_migration_generator.rb
@@ -1,4 +1,5 @@
 require 'rails/generators/active_record'
+require 'active_support/core_ext/object/inclusion'
 
 module ActiveRecord
   module Generators
@@ -13,7 +14,7 @@ def create_migration_file
 
         def session_table_name
           current_table_name = ActiveRecord::SessionStore::Session.table_name
-          if ["sessions", "session"].include?(current_table_name)
+          if current_table_name.either?("sessions", "session")
             current_table_name = (ActiveRecord::Base.pluralize_table_names ? 'session'.pluralize : 'session')
           end
           current_table_name
diff --git a/activerecord/test/cases/associations/join_model_test.rb b/activerecord/test/cases/associations/join_model_test.rb
index 5a7b13903031b..afc830cae9e99 100644
--- a/activerecord/test/cases/associations/join_model_test.rb
+++ b/activerecord/test/cases/associations/join_model_test.rb
@@ -1,4 +1,5 @@
 require "cases/helper"
+require 'active_support/core_ext/object/inclusion'
 require 'models/tag'
 require 'models/tagging'
 require 'models/post'
@@ -453,7 +454,7 @@ def test_associating_unsaved_records_with_has_many_through
     assert saved_post.tags.include?(new_tag)
 
     assert new_tag.persisted?
-    assert saved_post.reload.tags(true).include?(new_tag)
+    assert new_tag.in?(saved_post.reload.tags(true))
 
 
     new_post = Post.new(:title => "Association replacmenet works!", :body => "You best believe it.")
@@ -466,7 +467,7 @@ def test_associating_unsaved_records_with_has_many_through
 
     new_post.save!
     assert new_post.persisted?
-    assert new_post.reload.tags(true).include?(saved_tag)
+    assert saved_tag.in?(new_post.reload.tags(true))
 
     assert !posts(:thinking).tags.build.persisted?
     assert !posts(:thinking).tags.new.persisted?
diff --git a/activerecord/test/cases/attribute_methods/read_test.rb b/activerecord/test/cases/attribute_methods/read_test.rb
index d0a90282646cb..3641031d12cba 100644
--- a/activerecord/test/cases/attribute_methods/read_test.rb
+++ b/activerecord/test/cases/attribute_methods/read_test.rb
@@ -1,4 +1,5 @@
 require "cases/helper"
+require 'active_support/core_ext/object/inclusion'
 
 module ActiveRecord
   module AttributeMethods
@@ -41,13 +42,13 @@ def test_define_attribute_methods
         instance = @klass.new
 
         @klass.column_names.each do |name|
-          assert ! instance.methods.map(&:to_s).include?(name)
+          assert !name.in?(instance.methods.map(&:to_s))
         end
 
         @klass.define_attribute_methods
 
         @klass.column_names.each do |name|
-          assert(instance.methods.map(&:to_s).include?(name), "#{name} is not defined")
+          assert name.in?(instance.methods.map(&:to_s)), "#{name} is not defined"
         end
       end
 
diff --git a/activerecord/test/cases/attribute_methods_test.rb b/activerecord/test/cases/attribute_methods_test.rb
index 84f75cc803fb3..aaf2435cd986b 100644
--- a/activerecord/test/cases/attribute_methods_test.rb
+++ b/activerecord/test/cases/attribute_methods_test.rb
@@ -1,4 +1,5 @@
 require "cases/helper"
+require 'active_support/core_ext/object/inclusion'
 require 'models/minimalistic'
 require 'models/developer'
 require 'models/auto_id'
@@ -638,7 +639,7 @@ def cached_columns
   end
 
   def time_related_columns_on_topic
-    Topic.columns.select { |c| [:time, :date, :datetime, :timestamp].include?(c.type) }
+    Topic.columns.select { |c| c.type.either?(:time, :date, :datetime, :timestamp) }
   end
 
   def serialized_columns_on_topic
diff --git a/activerecord/test/cases/defaults_test.rb b/activerecord/test/cases/defaults_test.rb
index deaf5252db5bf..57709f0c71da2 100644
--- a/activerecord/test/cases/defaults_test.rb
+++ b/activerecord/test/cases/defaults_test.rb
@@ -1,4 +1,5 @@
 require "cases/helper"
+require 'active_support/core_ext/object/inclusion'
 require 'models/default'
 require 'models/entrant'
 
@@ -94,7 +95,7 @@ def test_mysql_integer_not_null_defaults
       assert_equal 0, klass.columns_hash['zero'].default
       assert !klass.columns_hash['zero'].null
       # 0 in MySQL 4, nil in 5.
-      assert [0, nil].include?(klass.columns_hash['omit'].default)
+      assert klass.columns_hash['omit'].default.either?(0, nil)
       assert !klass.columns_hash['omit'].null
 
       assert_raise(ActiveRecord::StatementInvalid) { klass.create! }
diff --git a/activeresource/lib/active_resource/connection.rb b/activeresource/lib/active_resource/connection.rb
index 480f2fbecbae7..09d0659b438e4 100644
--- a/activeresource/lib/active_resource/connection.rb
+++ b/activeresource/lib/active_resource/connection.rb
@@ -1,5 +1,6 @@
 require 'active_support/core_ext/benchmark'
 require 'active_support/core_ext/uri'
+require 'active_support/core_ext/object/inclusion'
 require 'net/https'
 require 'date'
 require 'time'
@@ -277,7 +278,7 @@ def http_format_header(http_method)
       def legitimize_auth_type(auth_type)
         return :basic if auth_type.nil?
         auth_type = auth_type.to_sym
-        [:basic, :digest].include?(auth_type) ? auth_type : :basic
+        auth_type.either?(:basic, :digest) ? auth_type : :basic
       end
   end
 end
diff --git a/activeresource/lib/active_resource/http_mock.rb b/activeresource/lib/active_resource/http_mock.rb
index 75649053d0284..e085a05f6d0bd 100644
--- a/activeresource/lib/active_resource/http_mock.rb
+++ b/activeresource/lib/active_resource/http_mock.rb
@@ -1,4 +1,5 @@
 require 'active_support/core_ext/kernel/reporting'
+require 'active_support/core_ext/object/inclusion'
 
 module ActiveResource
   class InvalidRequestError < StandardError; end #:nodoc:
@@ -299,7 +300,7 @@ def initialize(body, message = 200, headers = {})
     end
 
     def success?
-      (200..299).include?(code)
+      code.in?(200..299)
     end
 
     def [](key)
diff --git a/activeresource/test/cases/http_mock_test.rb b/activeresource/test/cases/http_mock_test.rb
index 43cf5f5ef0d32..542ce38ba3e43 100644
--- a/activeresource/test/cases/http_mock_test.rb
+++ b/activeresource/test/cases/http_mock_test.rb
@@ -1,4 +1,5 @@
 require 'abstract_unit'
+require 'active_support/core_ext/object/inclusion'
 
 class HttpMockTest < ActiveSupport::TestCase
   setup do
@@ -192,7 +193,7 @@ class HttpMockTest < ActiveSupport::TestCase
   end
 
   def request(method, path, headers = {}, body = nil)
-    if [:put, :post].include? method
+    if method.either?(:put, :post)
       @http.send(method, path, body, headers)
     else
       @http.send(method, path, headers)
diff --git a/activesupport/bin/generate_tables b/activesupport/bin/generate_tables
index 5fefa429df958..0ca2f52363ec8 100644
--- a/activesupport/bin/generate_tables
+++ b/activesupport/bin/generate_tables
@@ -105,7 +105,7 @@ module ActiveSupport
 
         def normalize_boundary_map
           @ucd.boundary.each do |k,v|
-            if [:lf, :cr].include? k
+            if k.in(:lf, :cr)
               @ucd.boundary[k] = v[0]
             end
           end
diff --git a/activesupport/lib/active_support/cache/file_store.rb b/activesupport/lib/active_support/cache/file_store.rb
index 18182bbb40bf3..5eeb17efd52fa 100644
--- a/activesupport/lib/active_support/cache/file_store.rb
+++ b/activesupport/lib/active_support/cache/file_store.rb
@@ -1,5 +1,6 @@
 require 'active_support/core_ext/file/atomic'
 require 'active_support/core_ext/string/conversions'
+require 'active_support/core_ext/object/inclusion'
 require 'rack/utils'
 
 module ActiveSupport
@@ -20,7 +21,7 @@ def initialize(cache_path, options = nil)
       end
 
       def clear(options = nil)
-        root_dirs = Dir.entries(cache_path).reject{|f| ['.', '..'].include?(f)}
+        root_dirs = Dir.entries(cache_path).reject{|f| f.either?('.', '..')}
         FileUtils.rm_r(root_dirs.collect{|f| File.join(cache_path, f)})
       end
 
@@ -161,7 +162,7 @@ def file_path_key(path)
         # Delete empty directories in the cache.
         def delete_empty_directories(dir)
           return if dir == cache_path
-          if Dir.entries(dir).reject{|f| ['.', '..'].include?(f)}.empty?
+          if Dir.entries(dir).reject{|f| f.either?('.', '..')}.empty?
             File.delete(dir) rescue nil
             delete_empty_directories(File.dirname(dir))
           end
diff --git a/activesupport/lib/active_support/callbacks.rb b/activesupport/lib/active_support/callbacks.rb
index 418102352fc96..738ce0e994e53 100644
--- a/activesupport/lib/active_support/callbacks.rb
+++ b/activesupport/lib/active_support/callbacks.rb
@@ -4,6 +4,7 @@
 require 'active_support/core_ext/class/attribute'
 require 'active_support/core_ext/kernel/reporting'
 require 'active_support/core_ext/kernel/singleton_class'
+require 'active_support/core_ext/object/inclusion'
 
 module ActiveSupport
   # \Callbacks are code hooks that are run at key points in an object's lifecycle.
@@ -412,7 +413,7 @@ def #{name}() #{str} end
       # CallbackChain.
       #
       def __update_callbacks(name, filters = [], block = nil) #:nodoc:
-        type = [:before, :after, :around].include?(filters.first) ? filters.shift : :before
+        type = filters.first.either?(:before, :after, :around) ? filters.shift : :before
         options = filters.last.is_a?(Hash) ? filters.pop : {}
         filters.unshift(block) if block
 
diff --git a/activesupport/lib/active_support/time_with_zone.rb b/activesupport/lib/active_support/time_with_zone.rb
index d3937154f76fc..3b053d783064e 100644
--- a/activesupport/lib/active_support/time_with_zone.rb
+++ b/activesupport/lib/active_support/time_with_zone.rb
@@ -1,5 +1,6 @@
 require "active_support/values/time_zone"
 require 'active_support/core_ext/object/acts_like'
+require 'active_support/core_ext/object/inclusion'
 
 module ActiveSupport
   # A Time-like class that can represent a time in any time zone. Necessary because standard Ruby Time instances are
@@ -344,7 +345,7 @@ def transfer_time_values_to_utc_constructor(time)
       end
 
       def duration_of_variable_length?(obj)
-        ActiveSupport::Duration === obj && obj.parts.any? {|p| [:years, :months, :days].include? p[0] }
+        ActiveSupport::Duration === obj && obj.parts.any? {|p| p[0].either?(:years, :months, :days) }
       end
   end
 end
diff --git a/activesupport/test/transliterate_test.rb b/activesupport/test/transliterate_test.rb
index b054855d0870b..09271b759d456 100644
--- a/activesupport/test/transliterate_test.rb
+++ b/activesupport/test/transliterate_test.rb
@@ -1,6 +1,7 @@
 # encoding: utf-8
 require 'abstract_unit'
 require 'active_support/inflector/transliterate'
+require 'active_support/core_ext/object/inclusion'
 
 class TransliterateTest < Test::Unit::TestCase
 
@@ -15,7 +16,7 @@ def test_transliterate_should_approximate_ascii
     # create string with range of Unicode"s western characters with
     # diacritics, excluding the division and multiplication signs which for
     # some reason or other are floating in the middle of all the letters.
-    string = (0xC0..0x17E).to_a.reject {|c| [0xD7, 0xF7].include? c}.pack("U*")
+    string = (0xC0..0x17E).to_a.reject {|c| c.either?(0xD7, 0xF7)}.pack("U*")
     string.each_char do |char|
       assert_match %r{^[a-zA-Z']*$}, ActiveSupport::Inflector.transliterate(string)
     end
diff --git a/railties/guides/rails_guides/textile_extensions.rb b/railties/guides/rails_guides/textile_extensions.rb
index affef1ccb08b7..f1486a7c10a29 100644
--- a/railties/guides/rails_guides/textile_extensions.rb
+++ b/railties/guides/rails_guides/textile_extensions.rb
@@ -1,9 +1,11 @@
+require 'active_support/core_ext/object/inclusion'
+
 module RailsGuides
   module TextileExtensions
     def notestuff(body)
       body.gsub!(/^(IMPORTANT|CAUTION|WARNING|NOTE|INFO)[.:](.*)$/) do |m|
         css_class = $1.downcase
-        css_class = 'warning' if ['caution', 'important'].include?(css_class)
+        css_class = 'warning' if css_class.either?('caution', 'important')
 
         result = "<div class='#{css_class}'><p>"
         result << $2.strip
@@ -33,7 +35,7 @@ def plusplus(body)
     def code(body)
       body.gsub!(%r{<(yaml|shell|ruby|erb|html|sql|plain)>(.*?)</\1>}m) do |m|
         es = ERB::Util.h($2)
-        css_class = ['erb', 'shell'].include?($1) ? 'html' : $1
+        css_class = $1.either?('erb', 'shell') ? 'html' : $1
         %{<notextile><div class="code_container"><code class="#{css_class}">#{es}</code></div></notextile>}
       end
     end
diff --git a/railties/lib/rails/commands.rb b/railties/lib/rails/commands.rb
index 02ccdf80601f9..28dff2389039e 100644
--- a/railties/lib/rails/commands.rb
+++ b/railties/lib/rails/commands.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/object/inclusion'
+
 ARGV << '--help' if ARGV.empty?
 
 aliases = {
@@ -69,7 +71,7 @@
   require 'rails/commands/application'
 
 else
-  puts "Error: Command not recognized" unless %w(-h --help).include?(command)
+  puts "Error: Command not recognized" unless command.either?('-h', '--help')
   puts <<-EOT
 Usage: rails COMMAND [ARGS]
 
diff --git a/railties/lib/rails/commands/application.rb b/railties/lib/rails/commands/application.rb
index 3b57b925ba223..20eb8b485ec8a 100644
--- a/railties/lib/rails/commands/application.rb
+++ b/railties/lib/rails/commands/application.rb
@@ -1,5 +1,7 @@
 require 'rails/version'
-if %w(--version -v).include? ARGV.first
+require 'active_support/core_ext/object/inclusion'
+
+if ARGV.first.either?('--version', '-v')
   puts "Rails #{Rails::VERSION::STRING}"
   exit(0)
 end
diff --git a/railties/lib/rails/commands/benchmarker.rb b/railties/lib/rails/commands/benchmarker.rb
index 0432261802e8e..ecdcccfd8d9bf 100644
--- a/railties/lib/rails/commands/benchmarker.rb
+++ b/railties/lib/rails/commands/benchmarker.rb
@@ -1,4 +1,6 @@
-if [nil, "-h", "--help"].include?(ARGV.first)
+require 'active_support/core_ext/object/inclusion'
+
+if ARGV.first.either?(nil, "-h", "--help")
   puts "Usage: rails benchmarker [times] 'Person.expensive_way' 'Person.another_expensive_way' ..."
   exit 1
 end
diff --git a/railties/lib/rails/commands/destroy.rb b/railties/lib/rails/commands/destroy.rb
index db59cd8ad9de6..829d29dad7137 100644
--- a/railties/lib/rails/commands/destroy.rb
+++ b/railties/lib/rails/commands/destroy.rb
@@ -1,7 +1,9 @@
 require 'rails/generators'
+require 'active_support/core_ext/object/inclusion'
+
 Rails::Generators.configure!
 
-if [nil, "-h", "--help"].include?(ARGV.first)
+if ARGV.first.either?(nil, "-h", "--help")
   Rails::Generators.help 'destroy'
   exit
 end
diff --git a/railties/lib/rails/commands/generate.rb b/railties/lib/rails/commands/generate.rb
index 1b3eef504ac0b..bef4c6df14888 100644
--- a/railties/lib/rails/commands/generate.rb
+++ b/railties/lib/rails/commands/generate.rb
@@ -1,7 +1,9 @@
 require 'rails/generators'
+require 'active_support/core_ext/object/inclusion'
+
 Rails::Generators.configure!
 
-if [nil, "-h", "--help"].include?(ARGV.first)
+if ARGV.first.either?(nil, "-h", "--help")
   Rails::Generators.help 'generate'
   exit
 end
diff --git a/railties/lib/rails/commands/profiler.rb b/railties/lib/rails/commands/profiler.rb
index 6d9717b5cdf0c..baa3baaec06af 100644
--- a/railties/lib/rails/commands/profiler.rb
+++ b/railties/lib/rails/commands/profiler.rb
@@ -1,4 +1,6 @@
-if [nil, "-h", "--help"].include?(ARGV.first)
+require 'active_support/core_ext/object/inclusion'
+
+if ARGV.first.either?(nil, "-h", "--help")
   $stderr.puts "Usage: rails profiler 'Person.expensive_method(10)' [times] [flat|graph|graph_html]"
   exit(1)
 end
diff --git a/railties/lib/rails/generators/base.rb b/railties/lib/rails/generators/base.rb
index dfecd2a6e4b21..e2c19340f4b2f 100644
--- a/railties/lib/rails/generators/base.rb
+++ b/railties/lib/rails/generators/base.rb
@@ -8,6 +8,7 @@
 end
 
 require 'rails/generators/actions'
+require 'active_support/core_ext/object/inclusion'
 
 module Rails
   module Generators
@@ -164,7 +165,7 @@ def self.hook_for(*names, &block)
         names.each do |name|
           defaults = if options[:type] == :boolean
             { }
-          elsif [true, false].include?(default_value_for_option(name, options))
+          elsif default_value_for_option(name, options).either?(true, false)
             { :banner => "" }
           else
             { :desc => "#{name.to_s.humanize} to be invoked", :banner => "NAME" }
diff --git a/railties/lib/rails/generators/generated_attribute.rb b/railties/lib/rails/generators/generated_attribute.rb
index 64273e4ca429c..8ed3b18872727 100644
--- a/railties/lib/rails/generators/generated_attribute.rb
+++ b/railties/lib/rails/generators/generated_attribute.rb
@@ -1,4 +1,5 @@
 require 'active_support/time'
+require 'active_support/core_ext/object/inclusion'
 
 module Rails
   module Generators
@@ -44,7 +45,7 @@ def human_name
       end
 
       def reference?
-        [ :references, :belongs_to ].include?(self.type)
+        self.type.either?(:references, :belongs_to)
       end
     end
   end