1. a putative logical error that occurs when an attempt is made to define values in terms of natural properties. Values such as goodness and truth are held to be human perceptions and to have no ontological status, or independent existence, as properties of things.

2. more specifically, the fallacy of basing a moral conclusion (i.e., a conclusion about what ought to be) on ontological premises (i.e., premises about what is or is not the case). An example would be arguing that war is morally acceptable because wars have occurred throughout history. Not all philosophers would agree that all such arguments are necessarily fallacious. [identified by British philosopher George Edward Moore (1873–1958)]