The International Phonetic Alphabet (IPA) possesses a variety of obsolete and nonstandard symbols. Throughout the history of the IPA, characters representing phonetic values have been modified or completely replaced. An example is ⟨ɷ⟩ for standard [ʊ]. Several symbols indicating secondary articulation have been dropped altogether, with the idea that they should be indicated with diacritics: ⟨ʮ⟩ for [z̩ʷ] is one. In addition, the rare voiceless implosive series ⟨ƥ ƭ 𝼉 ƈ ƙ ʠ⟩ has been dropped.
Other characters have been added in for specific phonemes which do not possess a specific symbol in the IPA. Those studying modern Chinese phonology have used ⟨ɿ⟩ to represent the sound of -i in Pinyin hanzi which has been variously described as [ɨ], [ɹ̩], [z̩] or [ɯ]. (See the sections Vowels and Syllabic consonants of the article Standard Chinese phonology.) The term para-IPA is used to describe "symbols that are commonly used within IPA notation but that are not themselves part of the IPA alphabet."
