To further clarify this point, consider the following. First, it is never possible to provide any absolute scientific proof for the truth of "any" particular concept of economic value in economics, because the attribution of economic value itself always involves human and moral interpretations that go beyond facts and logic. By nature, the concept of economic value is not a scientifically provable concept but an assumption. Marx himself explicitly ridiculed the idea that he should be required to "prove his concept of value".