In general, a full letter of an abugida transcribes a consonant. Full letters are written in a linear sequence in a consistent direction. Vowels are dependent on the consonant. They are written through modification of the consonant letter, either by means of diacritics which are placed in a vowel-dependent position relative to the consonant (rather than always progressing in the same direction as the sequence of full letters) or through changes in the form of the consonant itself.
Vowels not preceded by a consonant may be represented with:
Consonants not followed by a vowel may be represented with:
The term abugida was adopted into English as a linguistic term by Peter T. Daniels. It is the colloquial name of the Ge‘ez script, derived from the first four letters aləf, bet, gäməl, dənt (in the biblical A B G D order of Hebrew) graded by the first four vowel forms, much as the term abecedary is derived from the Latin a be ce de. As Daniels used the word, an abugida contrasts with a syllabary, where letters with shared consonants or vowels show no particular resemblance to each another, and with an alphabet proper, where independent letters are used to denote both consonants and vowels. Traditionally, abugidas have been considered to be syllabaries or intermediate between syllabaries and alphabets ("semi-syllabaries", "alpha-syllabaries", etc.). Less formally, however, abugidas are simply called "alphabets".
|Feature||North Indic||South Indic||Ethiopic||Canadian||Thaana|
|Vowel after consonant||Dependent sign|
| Change shape|
|Rotation or reflection|| Dependent sign|
|Initial vowel letter(s)||Full letters||Zero consonant||Glottal stop||Zero consonant|
|Absence of vowel sign||[ə], [ɔ], [a], or [o]||[ə]||Vowel indication obligatory|
|Virama (zero vowel sign)||Often||Consistently||None||Always|
|Consonant ligatures||Often||Few or none||None|
|Final consonant dependents||Usually ṃ, ḥ only||No||Yes (all)||No|
|Distinct final forms||ṃ, ḥ only||N/A||Western only||N/A|
|Final consonant position||Top or inline||Inline||N/A||Inline, small, raised||N/A|
Indic scripts originated in South Asia and spread to Southeast Asia. All surviving Indic scripts are descendants of the Brahmi alphabet. Today they are used in most languages of South Asia (except Urdu and other languages of Pakistan) and mainland Southeast Asia (Burma, Thailand, Laos, Cambodia; but not Malaysia or Vietnam). The primary division is into North Indic scripts used in North India, Nepal, Tibet, Bhutan and South Indic scripts used in South India, Sri Lanka, and Southeast Asia. South Indic letter forms are very rounded; North Indic less so, though Oriya, Golmol and Litumol of Nepal script are rounded. Most North Indic scripts' full letters incorporate a horizontal line at the top, with Gujarati script an exception; South Indic scripts do not.
Indic scripts indicate vowels through dependent vowel signs (diacritics) around the consonants, often including a sign that explicitly indicates the lack of a vowel. If a consonant has no vowel sign, this indicates a default vowel. Vowel diacritics may appear above, below, to the left, to the right, or around the consonant.
The most populous Indic script is Devanagari, used for Hindi, Bhojpuri, Marathi, Nepali, and often Sanskrit. A basic letter such as क represents a syllable with the default vowel, in this case ka ([kə]), or, in final position, a final consonant, in this case k. This inherent vowel may be changed by adding vowel marks (diacritics), producing syllables such as कि ki, कु ku, के ke, को ko. The mora a consonant letter represents, either with or without a marked vowel, is called an akshara.
In many of the Brahmic scripts, a syllable beginning with a cluster is treated as a single character for purposes of vowel marking, so a vowel marker like ि -i, falling before the character it modifies, may appear several positions before the place where it is pronounced. For example, the game cricket in Hindi is क्रिकेट krikeţ; the diacritic for /i/ appears before the consonant cluster /kr/, not before the /r/. A more unusual example is seen in the Batak alphabet: Here the syllable bim is written ba-ma-i-(virama). That is, the vowel diacritic and virama are both written after the consonants for the whole syllable.
In many abugidas, there is also a diacritic to suppress the inherent vowel, yielding the bare consonant. In Devanagari, क् is k, and ल् is l. This is called the virama in Sanskrit, or halant in Hindi. It may be used to form consonant clusters, or to indicate that a consonant occurs at the end of a word. For text information processing on computer, other means of expressing these functions include special conjunct forms in which two or more consonant characters are merged to express a cluster, such as Devanagari: क्ल kla. (Note that on some fonts display this as क् followed by ल, rather than forming a conjunct. This expedient is used by ISCII and South Asian scripts of Unicode.) Thus a closed syllable such as kal requires two akshara to write.
The Róng script used for the Lepcha language goes further than other Indic abugidas, in that a single akshara can represent a closed syllable: Not only the vowel, but any final consonant is indicated by a diacritic. For example, the syllable [sok] would be written as something like s̥̽, here with an underring representing /o/ and an overcross representing the diacritic for final /k/. Most other Indic abugidas can only indicate a very limited set of final consonants with diacritics, such as /ŋ/ or /r/, if they can indicate any at all.
In the family known as Canadian Aboriginal syllabics, vowels are indicated by changing the orientation of the akshara. Each vowel has a consistent orientation; for example, Inuktitut ᐱ pi, ᐳ pu, ᐸ pa; ᑎ ti, ᑐ tu, ᑕ ta. Although there is a vowel inherent in each, all rotations have equal status and none can be identified as basic. Bare consonants are indicated either by separate diacritics, or by superscript versions of the aksharas; there is no vowel-killer mark.
In Ethiopic, which gave us the word abugida, the diacritics have fused to the consonants to the point that they must be considered modifications of the form of the letters. Children learn each modification separately, as in a syllabary; nonetheless, the graphic similarities between syllables with the same consonant is readily apparent, unlike the case in a true syllabary.
Though now an abugida, the Ge'ez alphabet was actually an abjad until the 4th century AD. In the Ge'ez abugida, the form of the letter itself may be altered. For example, ሀ hä [hə] (base form), ሁ hu (with a right-side diacritic that does not alter the letter), ሂ hi (with a subdiacritic that compresses the letter, so that the whole fidel occupies the same amount of space), ህ hə [hɨ] or [h] (where the letter is modified with a kink in the left arm).
The Arabic-alphabet scripts used for Kurdish in Iraq and for Uighur in Xinjiang, China are fully voweled, but since the vowels are full letters rather than diacritics, and there are no inherent vowels, these are considered alphabets rather than abugidas.
Most Indian and Indochinese abugidas appear to have first evolved from abjads with the Kharoṣṭhī and Brāhmī scripts; the abjad in question is usually considered to be the Aramaic one, but while the link between Aramaic and Kharosthi is more or less undisputed, this is not the case with Brahmi. The Kharosthi family does not survive today, but Brahmi's descendants include most of the modern scripts of South and Southeast Asia. Although Ge'ez derived from a different abjad, one theory is that its evolution into an abugida may have been influenced by Christian missionaries from India.