diff --git a/lib/cancan/ability.rb b/lib/cancan/ability.rb
index f1a45d5..1d1df1c 100644
--- a/lib/cancan/ability.rb
+++ b/lib/cancan/ability.rb
@@ -117,7 +117,7 @@ module CanCan
     #   can :read, :stats
     #   can? :read, :stats # => true
     #
-    def can(action, subject, conditions = nil, &block)
+    def can(action = nil, subject = nil, conditions = nil, &block)
       can_definitions << CanDefinition.new(true, action, subject, conditions, block)
     end
 
@@ -133,7 +133,7 @@ module CanCan
     #     product.invisible?
     #   end
     #
-    def cannot(action, subject, conditions = nil, &block)
+    def cannot(action = nil, subject = nil, conditions = nil, &block)
       can_definitions << CanDefinition.new(false, action, subject, conditions, block)
     end
 
diff --git a/lib/cancan/can_definition.rb b/lib/cancan/can_definition.rb
index e61dd94..dea8432 100644
--- a/lib/cancan/can_definition.rb
+++ b/lib/cancan/can_definition.rb
@@ -11,6 +11,7 @@ module CanCan
     # and subject respectively (such as :read, @project). The third argument is a hash
     # of conditions and the last one is the block passed to the "can" call.
     def initialize(base_behavior, action, subject, conditions, block)
+      @match_all = action.nil? && subject.nil?
       @base_behavior = base_behavior
       @actions = [action].flatten
       @subjects = [subject].flatten
@@ -20,12 +21,14 @@ module CanCan
 
     # Matches both the subject and action, not necessarily the conditions
     def relevant?(action, subject)
-      matches_action?(action) && matches_subject?(subject)
+      @match_all || (matches_action?(action) && matches_subject?(subject))
     end
 
     # Matches the block or conditions hash
     def matches_conditions?(action, subject, extra_args)
-      if @block && subject.class != Class
+      if @match_all
+        call_block_with_all(action, subject, extra_args)
+      elsif @block && subject.class != Class
         @block.call(subject, *extra_args)
       elsif @conditions.kind_of?(Hash) && subject.class != Class
         matches_conditions_hash?(subject)
@@ -91,5 +94,13 @@ module CanCan
         end
       end
     end
+    
+    def call_block_with_all(action, subject, extra_args)
+      if subject.class == Class
+        @block.call(action, subject, nil, *extra_args)
+      else
+        @block.call(action, subject.class, subject, *extra_args)
+      end
+    end
   end
 end
diff --git a/spec/cancan/ability_spec.rb b/spec/cancan/ability_spec.rb
index e23c7a3..9be365a 100644
--- a/spec/cancan/ability_spec.rb
+++ b/spec/cancan/ability_spec.rb
@@ -79,8 +79,10 @@ describe CanCan::Ability do
     @ability.can?(:increment, 123).should be_true
   end
 
-  it "should return block result and only pass object for any action" do
-    @ability.can :manage, :all do |object|
+  it "should always call block with arguments when passing no arguments to can" do
+    @ability.can do |action, object_class, object|
+      action.should == :foo
+      object_class.should == 123.class
       object.should == 123
       @block_called = true
     end
@@ -88,6 +90,17 @@ describe CanCan::Ability do
     @block_called.should be_true
   end
 
+  it "should pass nil to object when comparing class with can check" do
+    @ability.can do |action, object_class, object|
+      action.should == :foo
+      object_class.should == Hash
+      object.should be_nil
+      @block_called = true
+    end
+    @ability.can?(:foo, Hash)
+    @block_called.should be_true
+  end
+
   it "should automatically alias index and show into read calls" do
     @ability.can :read, :all
     @ability.can?(:index, 123).should be_true