diff --git a/activesupport/CHANGELOG b/activesupport/CHANGELOG
index 148feff061b38..f1e40389e9af0 100644
--- a/activesupport/CHANGELOG
+++ b/activesupport/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Add Object#acts_like? and Time#acts_like_time? and Date#acts_like_date? to facilitate duck-typing. [Jamis Buck]
+
 * Make 1.months and friends accurate by introducing a Duration class.  #6835 [eventualbuddha]
 
 * Document Inflector.ordinalize and merge docs from String inflections.  #7023 [smeade]
diff --git a/activesupport/lib/active_support/core_ext/date.rb b/activesupport/lib/active_support/core_ext/date.rb
index effb749c25503..9d9051dfbef58 100644
--- a/activesupport/lib/active_support/core_ext/date.rb
+++ b/activesupport/lib/active_support/core_ext/date.rb
@@ -1,8 +1,10 @@
 require 'date'
+require File.dirname(__FILE__) + '/date/behavior'
 require File.dirname(__FILE__) + '/date/calculations'
 require File.dirname(__FILE__) + '/date/conversions'
 
 class Date#:nodoc:
+  include ActiveSupport::CoreExtensions::Date::Behavior
   include ActiveSupport::CoreExtensions::Date::Calculations
   include ActiveSupport::CoreExtensions::Date::Conversions
 end
diff --git a/activesupport/lib/active_support/core_ext/date/behavior.rb b/activesupport/lib/active_support/core_ext/date/behavior.rb
new file mode 100644
index 0000000000000..011cc17cbf5bc
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/date/behavior.rb
@@ -0,0 +1,13 @@
+module ActiveSupport #:nodoc:
+  module CoreExtensions #:nodoc:
+    module Date #:nodoc:
+      module Behavior
+        # Enable more predictable duck-typing on Date-like classes. See
+        # Object#acts_like?.
+        def acts_like_date?
+          true
+        end
+      end
+    end
+  end
+end
diff --git a/activesupport/lib/active_support/core_ext/date_time.rb b/activesupport/lib/active_support/core_ext/date_time.rb
new file mode 100644
index 0000000000000..67463d2352740
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/date_time.rb
@@ -0,0 +1,5 @@
+require "#{File.dirname(__FILE__)}/time/behavior"
+
+class DateTime
+  include ActiveSupport::CoreExtensions::Time::Behavior
+end
\ No newline at end of file
diff --git a/activesupport/lib/active_support/core_ext/object/misc.rb b/activesupport/lib/active_support/core_ext/object/misc.rb
index ea8e3a1d6a32a..aae336e6f4e73 100644
--- a/activesupport/lib/active_support/core_ext/object/misc.rb
+++ b/activesupport/lib/active_support/core_ext/object/misc.rb
@@ -31,4 +31,13 @@ def with_options(options)
   def to_json
     ActiveSupport::JSON.encode(self)
   end
+
+  # A duck-type assistant method. For example, ActiveSupport extends Date
+  # to define an acts_like_date? method, and extends Time to define
+  # acts_like_time?. As a result, we can do "x.acts_like?(:time)" and
+  # "x.acts_like?(:date)" to do duck-type-safe comparisons, since classes that
+  # we want to act like Time simply need to define an acts_like_time? method.
+  def acts_like?(duck)
+    respond_to? :"acts_like_#{duck}?"
+  end
 end
\ No newline at end of file
diff --git a/activesupport/lib/active_support/core_ext/time.rb b/activesupport/lib/active_support/core_ext/time.rb
index 9e3c7a032937f..a802c065a76e6 100644
--- a/activesupport/lib/active_support/core_ext/time.rb
+++ b/activesupport/lib/active_support/core_ext/time.rb
@@ -1,7 +1,9 @@
+require File.dirname(__FILE__) + '/time/behavior'
 require File.dirname(__FILE__) + '/time/calculations'
 require File.dirname(__FILE__) + '/time/conversions'
 
 class Time#:nodoc:
+  include ActiveSupport::CoreExtensions::Time::Behavior
   include ActiveSupport::CoreExtensions::Time::Calculations
   include ActiveSupport::CoreExtensions::Time::Conversions
 end
diff --git a/activesupport/lib/active_support/core_ext/time/behavior.rb b/activesupport/lib/active_support/core_ext/time/behavior.rb
new file mode 100644
index 0000000000000..a5c0baacdf609
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/time/behavior.rb
@@ -0,0 +1,13 @@
+module ActiveSupport #:nodoc:
+  module CoreExtensions #:nodoc:
+    module Time #:nodoc:
+      module Behavior
+        # Enable more predictable duck-typing on Time-like classes. See
+        # Object#acts_like?.
+        def acts_like_time?
+          true
+        end
+      end
+    end
+  end
+end
diff --git a/activesupport/test/core_ext/object_and_class_ext_test.rb b/activesupport/test/core_ext/object_and_class_ext_test.rb
index 9daf8d0ac4433..e48d87a198c74 100644
--- a/activesupport/test/core_ext/object_and_class_ext_test.rb
+++ b/activesupport/test/core_ext/object_and_class_ext_test.rb
@@ -96,6 +96,34 @@ def test_extend_with_included_modules_from
     assert object.respond_to?(:baz)
   end
 
+  class DuckTime
+    def acts_like_time?
+      true
+    end
+  end
+
+  def test_duck_typing
+    object = Object.new
+    time   = Time.now
+    date   = Date.today
+    dt     = DateTime.new
+    duck   = DuckTime.new
+
+    assert !object.acts_like?(:time)
+    assert !object.acts_like?(:date)
+
+    assert time.acts_like?(:time)
+    assert !time.acts_like?(:date)
+
+    assert !date.acts_like?(:time)
+    assert date.acts_like?(:date)
+
+    assert dt.acts_like?(:time)
+    assert dt.acts_like?(:date)
+
+    assert duck.acts_like?(:time)
+    assert !duck.acts_like?(:date)
+  end
 end
 
 class ObjectInstanceVariableTest < Test::Unit::TestCase