Sui generis (English pronunciation (IPA) [ˈs(j)uːaɪ ˈdʒɛnərɪs] or [ˈsuːɪ ˈdʒɛnərɪs]) is a (post) Latin expression, literally meaning of its own kind/genus or unique in its characteristics. The expression was effectively created by scholastic philosophy to indicate an idea, an entity or a reality that cannot be included in a wider concept, and in the structure genus > species a species that heads its own genus.
In law, it is a term of art used to identify a legal classification that exists independently of other categorizations because of its uniqueness or due to the specific creation of an entitlement or obligation. In intellectual property there are rights which are known as being sui generis to owners of a small class of works, such as intellectual property rights in mask works, ship hull designs, databases, or plant species.
In statutory interpretation, it refers to the problem of giving meaning to groups of words where one of the words is ambiguous or inherently unclear. For example, in Criminal Law, a statute might require a mens rea element of "unlawfully and maliciously". Whereas the word "maliciously" is well-understood, the word "unlawfully" in this context is less clear. Hence, it must be given a meaning of the "same kind" as the word of established meaning. This is particularly the case when the two or more words are conjoined, i.e. linked by the word "and", as opposed to placed in a disjunctive relationship, i.e. linked by the word "or", where the interpretation of the two or more words might be different depending on the circumstances (sometimes courts have to attribute a conjunctive intention to the legislature even though the list is disjunctive because, otherwise, no sensible overall interpretation can be ascribed).
In British town planning law, certain uses of land are labelled 'sui generis' to indicate that they are not covered by a 'Use Class' – effectively in a class of their own. Change of use of land within a Use Class does not require planning permission; however, changing between Use Classes, or any change of use of sui generis land, requires planning permission. Examples of sui generis use (identified in the Use Classes Order 1987) include theatres, amusement arcades, laundrettes, taxi or vehicle hire businesses, petrol filling stations, scrapyards.
In political science the unparallelled development of the European Union as compared to other international organizations has led to its designation as a sui generis geopolitical entity. The EU has often been described as "somewhere in between a confederation and a federation. A similar case which has led to the use of the label sui generis is the unique relationship between France and New Caledonia, since the legal status of New Caledonia can aptly be said to lie "somewhere between an overseas collectivity and a sovereign nation". Whereas there are perhaps other examples of such a status for other disputed or dependent territories, this arrangement is certainly unique within the French Republic.
In the sociology of Emile Durkheim "sui generis", is used to illustrate his theories on social existence. He maintains that society, as it was there before any living individual was born, is independent of all individuals. His "sui generis" (its closest English meaning in this sense being 'independent') society will furthermore continue its existence after the individual ceases to interact with it.