In cognitive lexical semantics, a linguistic unit such as a word is treated as being comprised of related senses or lexical concepts. The range of lexical concepts associated with a given word is assumed to form a network of senses which are related by degrees, with some lexical concepts being more central and others more peripheral. Accordingly, word senses are modelled in terms of creating a lattice structure, a semantic network, with a central sense, also known as a prototype.