Now, in metaphysics, a philosopher will often argue that some entity P is really nothing but Q. For example, heat is really nothing but the motion of molecules, the mind is really nothing but the brain, the color red is really nothing but the word red being used of an object or, perhaps, red is just a certain wavelength of light. At other times, a philosopher will argue that C is the very essence of D, that is, that D could not exist without C existing and being the very nature of what D is. For example, some have claimed that the very essence of the number two is to be the smallest even number greater than one, the nature of squareness is to be a shape, the essence of being a person is to be a material object, and the essence of existing is to be located at a place in space and time. In each of the examples cited, we can test the proposal it illustrates by using a thought experiment to suggest a _______ that runs contrary to the proposal in question. These thought experiments can be seen as attempts to state a possible world where one can _______. For example, if there is a possible world where there are minds without brains (say in a disembodied form of existence) or brains without minds (a zombie world), then the proposal that minds are nothing but brains is false. Furthermore, if C is offered as the very nature of D, then in every world where D exists, C must exist also. If we can state a possible world where _______, then C cannot be taken to be the essence of D. If C is "Uncle Larry's favorite number" and D is the number two, then there could be a world where D (the number two) exists but C does not (in worlds where Uncle Larry is dead or hates the number two). This possible world is a counterexample to the proposal in question. In metaphysical arguments concerning the essence of entities, What does a "counterexample" through a thought experiment primarily aim to achieve?
A)Proof of the entity's existence in the actual world
B)Demonstration of the entity's impossibility in any world
C)Confirmation of the entity's absolute necessity for existence
D)Challenge to the proposed essence or nature of the entity