The design claim is often challenged as an argument from ignorance, since it is often unexplained or unsupported, or explained by unscientific conjecture. Supporters of design assume that natural objects and man-made objects have similar properties, therefore both must be designed. However, different objects can have similar properties for different reasons, such as stars and light bulbs. Proponents must therefore demonstrate that "only" design can cause orderly systems or the argument is invalid.