1 files changed, 4 insertions, 3 deletions
diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index 74e2774626..f3f77e21c0 100644
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -75,13 +75,13 @@ module ActiveRecord
 
   class EagerLoadPolymorphicError < ActiveRecordError #:nodoc:
     def initialize(reflection)
-      super("Can not eagerly load the polymorphic association #{reflection.name.inspect}")
+      super("Cannot eagerly load the polymorphic association #{reflection.name.inspect}")
     end
   end
 
   class ReadOnlyAssociation < ActiveRecordError #:nodoc:
     def initialize(reflection)
-      super("Can not add to a has_many :through association. Try adding to #{reflection.through_reflection.name.inspect}.")
+      super("Cannot add to a has_many :through association. Try adding to #{reflection.through_reflection.name.inspect}.")
     end
   end
 
@@ -1213,7 +1213,8 @@ module ActiveRecord
       #   Returns the associated object. +nil+ is returned if none is found.
       # [association=(associate)]
       #   Assigns the associate object, extracts the primary key, sets it as the foreign key,
-      #   and saves the associate object.
+      #   and saves the associate object. To avoid database inconsistencies, permanently deletes an existing
+      #   associated object when assigning a new one, even if the new one isn't saved to database.
       # [build_association(attributes = {})]
       #   Returns a new object of the associated type that has been instantiated
       #   with +attributes+ and linked to this object through a foreign key, but has not