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In philosophy, universality is the notion that universal facts can be discovered and is therefore understood as being in opposition to relativism.
In certain religions, universalism is the quality ascribed to an entity whose existence is consistent throughout the universe. This article also discusses Kantian and Platonist notions of "universal", which are considered by many to be separate notions.
Universality in ethics
When used in the context of ethics, the meaning of universal refers to that which is true for "all similarly situated individuals." Rights, for example in natural rights, or in the 1789 Declaration of the Rights of Man and of the Citizen, for those heavily influenced by the philosophy of the Enlightenment and its conception of a human nature, could be considered universal. The 1948 Universal Declaration of Human Rights is inspired by such principles.
Universality in logic
In logic, or the consideration of valid arguments, a proposition is said to have universality if it can be conceived as being true in all possible contexts without creating a contradiction. Some philosophers have referred to such propositions as universalizable. Truth is considered to be universal if it is valid in all times and places. In this case, it is seen as eternal or as absolute. The relativist conception denies the existence of some or all universal truths, particularly ethical ones (through moral relativism). Mathematics is a field in which those truths discovered, in relation to the field of mathematics, are typically considered of universal scope. Though usage of the word truth has various domains of application, relativism does not necessarily apply to all of them. This is not to say that universality is limited to mathematics, for there exists a large number of people who apply the standard to philosophy, theology and beyond.
Universality in metaphysics
In metaphysics, a universal is a type, a property, or a relation. The noun universal contrasts with individual, while the adjective universal contrasts with particular or sometimes with concrete. The latter meaning, however, may be confusing since Hegelian and neo-Hegelian (e.g. British idealist) philosophies speak of concrete universals.
A universal may have instances, known as its particulars. For example, the type dog (or doghood) is a universal, as are the property red (or redness) and the relation betweenness (or being between). Any particular dog, red thing, or object that is between other things is not a universal, however, but is an instance of a universal. That is, a universal type (doghood), property (redness), or relation (betweenness) inheres a particular object (a specific dog, red thing, or object between other things).
Platonic realism holds universals to be the referents of general terms, i.e. the abstract, nonphysical entities to which words like "doghood", "redness", and "betweenness" refer. By contrast, particulars are the referents of proper names, like "Fido", or of definite descriptions that identify single objects, like the phrase, "that apple on the table". By contrast, other metaphysical theories merely use the terminology of universals to describe physical entities.
The problem of universals is an ancient problem in metaphysics concerning the nature of universals, or whether they exist. Part of the problem involves the implications of language use and the complexity of relating language to ontological theory.
Most ontological frameworks do not consider classes to be universals, although some prominent philosophers, such as John Bigelow, do.