A witness is an existing instance of a(see also copy). The witnesses form the evidence for the textual tradition of a given text, and are the basis from which stemmata are constructed. Witnesses may be carried in any physical medium; normally these will be manuscripts or printed books, but can also include oral recordings and the like in the case of folk tales and other oral traditions. A single manuscript is often witness to multiple texts, as manuscripts generally carry more than one text.
A distinction is normally drawn between a ‘direct witness’, which is an instance of the text observed directly in a document, and an ‘indirect witness', which may be a paraphrase, a translation, or even merely a reference to the text. Witnesses may be complete or incomplete, i.e. fragmentary or lacunary. Some scholars may also speak of a ‘conjectural witness’, which is not an extant textual witness but rather a postulated lost intermediary in a stemma.