Index: src/booc/App.cs
===================================================================
--- src/booc/App.cs	(revision 1446)
+++ src/booc/App.cs	(working copy)
@@ -292,6 +292,12 @@
 										break;
 									}
 									
+									case "ducky":
+									{
+										_options.DuckByDefault = true;
+										break;
+									}
+									
 									default:
 									{
 										InvalidOption(arg);								
Index: src/Boo.Lang.Compiler/TypeSystem/BooCodeBuilder.cs
===================================================================
--- src/Boo.Lang.Compiler/TypeSystem/BooCodeBuilder.cs	(revision 1446)
+++ src/Boo.Lang.Compiler/TypeSystem/BooCodeBuilder.cs	(working copy)
@@ -626,7 +626,7 @@
 					}
 					else
 					{
-						parameter.Type = CreateTypeReference(_tss.ObjectType);
+						parameter.Type = CreateTypeReference(_tss.DefaultType);
 					}
 				}
 				parameter.Entity = new InternalParameter(parameter, i + delta);
Index: src/Boo.Lang.Compiler/TypeSystem/TypeSystemServices.cs
===================================================================
--- src/Boo.Lang.Compiler/TypeSystem/TypeSystemServices.cs	(revision 1446)
+++ src/Boo.Lang.Compiler/TypeSystem/TypeSystemServices.cs	(working copy)
@@ -135,6 +135,8 @@
 		
 		CompilerContext _context;
 		
+		public IType DefaultType;
+		
 		public TypeSystemServices() : this(new CompilerContext())
 		{
 		}
@@ -189,9 +191,11 @@
 			Cache(IntPtrType = new ExternalType(this, Types.IntPtr));
 			Cache(MulticastDelegateType = new ExternalType(this, Types.MulticastDelegate));
 			Cache(DelegateType = new ExternalType(this, Types.Delegate));
+						
+			DefaultType = (Context.Parameters.DuckByDefault) ? DuckType : ObjectType;
 			
 			ObjectArrayType = GetArrayType(ObjectType);
-			
+
 			PreparePrimitives();
 		}
 		
@@ -225,12 +229,11 @@
 				return ICallableType;
 			}
 			
-			IType obj = ObjectType;			
 			if (current.IsClass && candidate.IsClass)
 			{
-				if (current ==  obj || candidate == obj)
+				if (current ==  DefaultType || candidate == DefaultType)
 				{
-					return obj;
+					return DefaultType;
 				}
 				if (current.GetTypeDepth() < candidate.GetTypeDepth())
 				{
@@ -238,7 +241,7 @@
 				}			
 				return GetMostGenericType(current, candidate.BaseType);
 			}			
-			return obj;
+			return DefaultType;
 		}
 		
 		public IType GetPromotedNumberType(IType left, IType right)
@@ -408,7 +411,7 @@
 					}
 				}
 			}
-			return ObjectType;
+			return DefaultType;
 		}
 		
 		public IType GetExpressionType(Expression node)
Index: src/Boo.Lang.Compiler/CompilerParameters.cs
===================================================================
--- src/Boo.Lang.Compiler/CompilerParameters.cs	(revision 1446)
+++ src/Boo.Lang.Compiler/CompilerParameters.cs	(working copy)
@@ -56,6 +56,8 @@
 		
 		bool _debug;
 		
+		bool _duckByDefault;
+		
 		public readonly TraceSwitch TraceSwitch = new TraceSwitch("booc", "boo compiler");
 
 		public CompilerParameters()
@@ -211,5 +213,18 @@
 				_debug = value;
 			}
 		}
+		
+		public bool DuckByDefault
+		{
+			get
+			{
+				return _duckByDefault;
+			}
+			
+			set
+			{
+				_duckByDefault = value;
+			}
+		}
 	}
 }