When the conclusion expresses what ought to be, based only on what is, or what ought not to be, based on what is not. This is very common, and most people never see the problem with these kinds of assertions due to accepted social and moral norms.
Examples:
- _Homosexuality is / ought to be morally wrong (moral property) because it is not normal (natural property).
or
Homosexuality is not normal (natural property); therefore, it is / ought to be morally wrong (moral property)._
Synonyms: is-ought fallacy, arguing from is to ought, is-should fallacy