Hypostatization

Sometimes related to the Four Terms Fallacy, this is treating an abstract idea as a physical object. For example, "Eating ice cream feels good. Therefore, we should give ice cream to criminals, so they become good." This assumes that "good" is a thing that can be measured and which is a physical property of ice cream — in fact "good" is an unmeasurable and quite subjective concept. Similarly, you can't go down to the store and pick up a can of thought or a box of blue; they are attributes of things, but do not exist independently of them.

This is also called reification, concretism, hypostatization, or the fallacy of misplaced concreteness.

A variation is treating a thought experiment as a physically workable one; for example, imagining that one could use Schrödinger's box apparatus to actually cause quantum superposition of a cat.

Literature

 * Socrates' argument against hedonism in Gorgias is pretty much entirely composed of this. Especially memorable is the bit where he gets the guy to agree that punishing criminals is correct, and that therefore one who punishes does good things, and therefore a criminal has good things done to him and his lot is made better.

Web Comics

 * Saturday Morning Breakfast Cereal had fun with this idea. Also, when the Zorblaxians were reading the Socratic Dialogues.