The word 'anagnorisis' - pronounced with the stress on the third syllable, 'an-ag-NORE-iss-iss', IPA: /,ænəg'nɒrɪsɪs/ - is used in the discussion of tragic drama to refer to the discovery or recognition by the protagonist of some crucial fact, usually the identity of another character, which leads to a change in his or her fortunes. (The plural of 'anagnorisis' is 'anagnorises', 'an-ag-NORE-iss-eez', IPA: /ænəg'nɒrɪ,siːz/ )
The word 'anagnorisis' is a transliteration of the ancient Greek word ἀναγνώρισις‚ (anagnorisis), which means 'recognition' and is one of the nouns from the verb ἀναγνωρίζειν (anagnorizein, to recognise). It was first used in the context of literary theory by the Greek philosopher Aristotle, who in ch. 10 of his Poetics distinguishes between 'simple' (ἁπλοι, haploi) and 'complex' (πεπλεγμένοι, peplegmenoi) plots by saying that in simple plots the action proceeds without a peripeteia (i.e., a sudden reversal of fortune) or an anagnorisis whereas in complex plots the action involves either a peripeteia or an anagnorisis or both (1452a14-18).
Aristotle defines anagnorisis in Poetics ch. 11 (1452a29-32) as a change from ignorance to knowledge, leading to friendship or enmity, of those who have been marked out for good or bad fortune, adding that the finest instances of anagnorisis are those in which it is accompanied by a peripeteia (1452a32-33). In Poetics ch. 16 he distinguishes a number of different kinds of anagnorisis on the basis of the different ways in which the recognition comes about: e.g., is the true identity of a character revealed by one of his or her physical features (such as a tell-tale scar or birthmark), or by a remark which he or she makes, or by an inference from some fact about the situation? He says that the best anagnorises are those in which the recognition occurs naturally through the development of the plot (1455a16-20).
It has sometimes been disputed whether anagnorisis is confined to the recognition of the true identity of persons or should be understood more broadly to include recognition of the truth about other matters, e.g., the nature of the circumstances in which the protagonist finds himself (or herself) or the consequences of a proposed course of action. The definition at the beginning of Poetics ch. 11 is arguably compatible with either interpretation, and Aristotle would certainly have been familiar with tragedies in which the peripeteia involves the realisation of the truth about some matter other than the true identity of another character - e.g., in Sophocles' Trachiniae (Women of Trachis) the peripeteia involves Deianeira's realisation that the ointment she thought was a love-charm and smeared on the tunic she sent to her husband Heracles, was in fact a deadly poison. However, most of the time, and very clearly in ch. 16, Aristotle seems to understand anagnorisis more narrowly as the recognition of a person's true identity.