Raised and lowered vowels

In the case of a vowel, raising means that the vowel is closer, toward the top of the vowel chart. For example, [e̝] represents a vowel somewhere between cardinal [e] and [i], or may even be [i]. Lowering, on the other hand, means that the vowel is more open, toward the bottom of the chart. For example, [e̞] represents a vowel somewhere between cardinal [e] and [ɛ], or may even be [ɛ].

In other non-IPA transcription systems, raised vowels are indicated with the iconic upward-pointing arrowhead U+02F0 ˰ MODIFIER LETTER LOW UP ARROWHEAD while lowered vowels have the downward arrowhead U+02EF ˯ MODIFIER LETTER LOW DOWN ARROWHEAD. Thus, IPA [e̝] is equivalent to [e˰], IPA [e̞] is equivalent to [e˯].

Raised and lowered consonants

With consonants, raising and lowering changes the manner of articulation to have more or less stricture. For example, raised approximants and trills are fricatives, whereas lowered fricatives are approximants. The ambiguous symbols for rear approximant/fricatives may be specified as fricatives with the raising diacritic, [ʁ̝, ʕ̝, ʢ̝], or as approximants with the lowering diacritic, [ʁ̞, ʕ̞, ʢ̞]. In Spanish, the lenited allophones of the voiced stops are generally transcribed as fricatives even though they are approximants, or intermediate between fricative and approximant. This may be partially due to the fact there is only a dedicated IPA symbol for one of them, the velar approximant. More precise transcription will use the fricative symbols with the lowering diacritic, [β̞, ð̞, ɣ˕] (the last symbol may be rendered as [ɣ̞], but that may not display properly in some browsers). Czech, on the other hand, requires the opposite: Its fricated trill, which is a separate phoneme, may be transcribed as a raised trill, [r̝]. Similarly, the non-sibilant coronal fricative is written [ɹ̝], and the voiceless velar lateral fricative as [ʟ̝̊]. (A dedicated letter for this sound, ⟨𝼄⟩, is provided by the extIPA and may be used in IPA transcription.)

From most open (least stricture) to most close (most stricture), there are several independent relationships among speech sounds. Open vowel → mid vowel → close vowel → approximant → fricative → plosive is one; flap → stop is another; and trill → trilled fricative yet another. The IPA chart has been organized so that the raising diacritic moves the value of a letter through these series toward the top of the chart, and the lowering diacritic toward the bottom of the chart, but this only works for some of the consonants. While it would be convenient if all consonants could be so ordered, consonants are too diverse for a single dimension to capture their relationships. In addition, many of the points along the series may be nasalized or lateralized as well, and these parameters are independent of stricture.

Examples of stricture series

	Oral	Nasal	Flap	Trill	Lateral
Stop	ɟ	ɲ	d		t͡ɬ
Fricative	ʝ	ʝ̃		r̝	ɬ
Approximant / Vibrant	j	ȷ̃	ɾ	r	l̥
Close vowel	i	ĩ	(N/A)
Near-close vowel	e̝	ẽ̝
Close-mid vowel	e	ẽ
Mid vowel	e̞	ẽ̞
Open-mid vowel	ɛ	ɛ̃
Near-open vowel	æ	æ̃
Open vowel	a	ã

Centralized vowels

A centralized vowel is a vowel that is more central than some point of reference, or that has undergone a shift in this direction. The diacritic for this in the International Phonetic Alphabet is the diaeresis, U+0308 ̈ COMBINING DIAERESIS.

For example, to transcribe rounded and unrounded near-close central vowels, the symbols [ɪ̈, ʊ̈] may be used.

In other (non-IPA) transcription systems, ⟨ᵻ, ᵿ⟩ (or ⟨ɪ, ʊ⟩) will be seen instead of [ɪ̈, ʊ̈] (by analogy with [ɨ, ʉ]). Before the letters [ɘ, ɵ, ɜ, ɞ] were added to the IPA in 1993, the symbols [ë, ö, ɛ̈, ɔ̈] were used for these near-schwa values. [ë, ö, ɛ̈, ɔ̈] would now be assumed to represent articulations intermediate between [e, o, ɛ, ɔ] and [ɘ, ɵ, ɜ, ɞ]. Similarly, [ï, ÿ, ü, ɯ̈] would be intermediate between [i, y, u, ɯ] and [ɨ, ʉ].

However, since the IPA does not specify the exact amount of centralization that centralized vowels have, the symbols [ë, ö, ɛ̈, ɔ̈] and [ï, ÿ, ü, ɯ̈] can in modern transcriptions^[2] be used at times to transcribe fully central vowels, or vowels that have a variable amount of centralization.

In the majority of languages described as having an [a] (which denotes a front vowel), the vowel is actually central and therefore a more narrow transcription of it is [ä]. However, this symbol is not commonly used mainly because of the common practice of avoiding using diacritics wherever possible, and because very few languages contrast front and central open unrounded vowels.

Instead of the diacritic for centralization, the advanced or retracted diacritics may be used (an equivalent transcription of [ä] is retracted [a̠]), but the concept of centralization is convenient in cases where front and back vowels move toward each other, rather than all advancing or retracting in the same direction.

When a transcription system uses both the centralized and the advanced/retracted diacritics, generally the former indicates a more central vowel, so that e.g. [i̠] indicates an only slightly centralized (retracted) front vowel [i], whereas [ï] indicates a more centralized (retracted) front vowel, or even a fully central vowel (which, as stated above, has a dedicated IPA symbol [ɨ]).

Centralized semivowels

Semivowels can be centralized much like vowels; for instance, the semivowels corresponding to the close central vowels [ɨ, ʉ] can be written as centralized palatal semivowels [j̈, ɥ̈], or centralized velar semivowels [ɰ̈, ẅ]. The transcription [ɥ̈] vs. [ẅ] may also denote a distinction in the type of rounding, with the former symbol denoting a semivowel with compressed rounding typical of front vowels, and the latter symbol denoting a semivowel with protruded rounding typical of central and back vowels, though an additional verbal clarification is usual in such cases, as the IPA does not provide any official means to distinguish sounds with compressed and protruded rounding.

Mid-centralized vowels

Mid-centralized vowels are closer to the midpoint of the vowel space than their referent vowels. That is, they are closer to the mid-central vowel schwa [ə] not just by means of centralization, but also by raising or lowering. The diacritic used to mark this in the International Phonetic Alphabet is the over-cross, U+033D ̽ COMBINING X ABOVE.

In most languages, vowels become mid-centralized when spoken quickly, and in some languages, such as English and Russian, many vowels are also mid-centralized when unstressed. This is a general characteristic of vowel reduction.

Even when fully articulated, the vowels of a language may be on the schwa side of a cardinal IPA vowel. One example of this is Lisbon Portuguese, where unstressed e is a near-close near-back unrounded vowel. That is, it lies between the close back unrounded vowel [ɯ] and schwa, where [ʊ] sits in the vowel chart, but unlike [ʊ], is not rounded. It may be written [ɯ̽], as in pegar [pɯ̽ˈɣaɾ] "to hold", though such a fully narrow transcription is rarely used, with symbols ⟨ɨ⟩ or ⟨ə⟩ (rarely: ⟨ɯ⟩) being the usual broader transcriptions.