Norms are concepts (sentences) of practical import, oriented to affecting an action, rather than conceptual abstractions that describe, explain, and express. Normative sentences imply "ought-to" types of statements and assertions, in distinction to sentences that provide "is" types of statements and assertions. Common normative sentences include commands, permissions, and prohibitions; common normative abstract concepts include sincerity, justification, and honesty. A popular account of norms describes them as reasons to take action, to believe, and to feel. Types of norms Orders and permissions express norms. Such norm sentences do not describe how the world is, they rather prescribe how the world should be. Imperative sentences are the most obvious way to express norms, but declarative sentences also may be norms, as is the case with laws or 'principles'. Generally, whether an expression is a norm depends on what the sentence intends to assert. For instance, a sentence of the form "All Ravens are Black" could on one account be taken as descriptive, in which case an instance of a white raven would contradict it, or alternatively "All Ravens are Black" could be interpreted as a norm, in which case it stands as a principle and definition, so 'a white raven' would then not be a raven. Those norms purporting to create obligations (or duties) and permissions are called deontic norms (see also deontic logic). The concept of deontic norm is already an extension of a previous concept of norm, which would only include imperatives, that is, norms purporting to create duties. The understanding that permissions are norms in the same way was an important step in ethics and philosophy of law. In addition to deontic norms, many other varieties have been identified. For instance, some constitutions establish the national anthem. These norms do not directly create any duty or permission. They create a "national symbol". Other norms create nations themselves or political and administrative regions within a nation. The action orientation of such norms is less obvious than in the case of a command or permission, but is essential for understanding the relevance of issuing such norms: When a folk song becomes a "national anthem" the meaning of singing one and the same song changes; likewise, when a piece of land becomes an administrative region, this has legal consequences for many activities taking place on that territory; and without these consequences concerning action, the norms would be irrelevant. A more obviously