The name Afro-Asiatic gained wide acceptance following the classification of African languages proposed in 1955–63 by the American linguist Joseph H. Greenberg (Greenberg, Joseph H.). Scholars in the former Soviet Union prefer to call these languages “Afrasian.” The name Hamito-Semitic (or Semito-Hamitic), although occasionally still used, is largely considered obsolete; many scholars reject it because it is linguistically wrong—there is no linguistic entity “Hamitic” to be contrasted, as a whole, to “Semitic.” Other designations, such as Erythraean and Lisramic, have gained little acceptance.

Speakers of Afro-Asiatic languages were among the first in human history to develop writing systems. Some Afro-Asiatic languages are known only from documents written as long as 5,000 years ago; examples include Akkadian (Akkadian language) and Eblaite (Eblaite language). Some have disappeared but left traces in the form of inscriptions; Old Libyan, for example, is found in inscriptions dated as early as 139 BCE. Others are mentioned in records that were transcribed in European languages, as is the case of the Guanche language of the Canary Islands. Coptic (Coptic language) represents a third case; it originated in antiquity and was spoken until the 16th or 17th century CE but is now represented only by a few liturgical phrases used within the Coptic Orthodox Church (Coptic Orthodox Church of Alexandria).

Certain similarities to Indo-European languages have prompted scholars to look for a special relationship between Afro-Asiatic and Indo-European. Some scholars even extend this kinship hypothesis to include the Uralic (Uralic languages), Altaic (Altaic languages), Kartvelian (Kartvelian languages), and Dravidian (Dravidian languages) language groups. Attempts have also been made to relate Afro-Asiatic to other African and European linguistic units, such as Niger-Congo (Niger-Congo languages), Nilo-Saharan (Nilo-Saharan languages), or Basque (Basque language). However, the common ancestor of these languages, if there was one, existed so long ago that it is almost impossible to apply sound comparative methods to modern languages in order to test this hypothesis.

Linguists use a set of methods with which they compare (comparative linguistics) languages, both modern and ancient, in order to establish “genetically related” language groups. The application of such methods involves the systematic analysis of the phonologies (phonology) (sound systems), vocabularies, and grammars of the languages in question. The products of such comparison are called “reconstructions” and are indicated by placing an asterisk * in front of the word or sound symbol; they describe a hypothetical common parent language (such as Proto-Afro-Asiatic) and its individual daughter languages (e.g., Proto-Chadic or Proto-Semitic), or a hypothetical common sound of origin. Languages are said to be genetically related when they meet two criteria: they match in phonology, vocabulary, and grammar in such a way that they can be systematically related to a common protolanguage, and the matches can be determined not to have resulted from chance resemblance or previous contact between genetically unrelated languages.

Solid comparative methods, although generally illuminating, are for several reasons difficult to apply to the languages and divisions within the Afro-Asiatic phylum. Relative chronology is one issue that makes applying such methods problematic. The vast majority of Afro-Asiatic languages are living languages without any written documents that would foster insights regarding the changes that inevitably occur over time. There are exceptions to this general rule; in some Semitic (Semitic languages) languages and Egyptian, there are documents that give linguists a picture of what these languages looked like—at least in written form—some 3,000–5,000 years ago. Using such attestations, Diakonoff classified Afro-Asiatic languages into Ancient, Middle, and Late Stage languages according to the extent to which they retained features of the ancestral protolanguage.

A second problem is referred to among linguists as “Semitic bias.” The languages within the Semitic family are relatively homogeneous, which has caused some scholars to identify the family with a set of characteristic speech sounds and features of grammar—a “Semitic type” that they believe extends beyond the limits of the family itself. In light of the great age of Semitic attestations, they carry this notion a step further, into the discussion of the hypothetical ancestral language. The result, at least for them, is that Proto-Afro-Asiatic comes to resemble a “Semitic type” language. Recent data from African Afro-Asiatic languages, however, tend not to confirm this theory.

A third complication relates to vowel usage in the phylum: most Afro-Asiatic languages do not indicate vowels within their written documents. This poses obvious problems for the identification and reconstruction of vocabulary and grammar.

Afro-Asiatic languages share features in phonetics and phonology, morphology, and syntax, as well as a fair number of cognate lexical items (i.e., words that have been retained from the common ancestral language). Given the great antiquity of Proto-Afro-Asiatic, only a few of its features can be expected to have survived in all divisions of Afro-Asiatic. Those that have include the feminine gender marker *t and the second-person marker *k. Other features or words of Proto-Afro-Asiatic show up only in languages of certain divisions or subdivisions.

Most Afro-Asiatic languages share a set, or inventory, of particular consonants (consonant). One group in this inventory is called the pharyngeal fricatives (fricative) and is exemplified in Egyptian, Cushitic (Cushitic languages), Amazigh (Amazigh languages), and Semitic by ħ and ʿ (“ayn”). A second commonly used group of consonants is an emphatic set, similar to the pharyngeal fricatives but with phonetically quite different articulations (articulation); characteristically, emphatics are formed deeper down in the vocal tract and may involve different airstream mechanisms.

Amazigh and Arabic have three major types of consonants: pharyngealized (articulated at the back of the vocal tract with the pharynx), velarized (in which the back of the tongue touches the soft palate), and uvularized (articulated at the back of the vocal tract with the uvula). In South Arabian, Ethio-Semitic, Cushitic, and Chadic (Chadic languages) languages, there are consonants characterized by the following “manners,” or types of air flow: explosive glottals, which occur when a complete closure is suddenly released; ejective glottals, which involve compressed air moving from the glottis and toward the lips; and implosive glottals, which involve air moving temporarily into the oral cavity before the release of the glottal closure allows the air from the lungs to stream out again. The glottal stop ʾ (“hamzah”) is used as a separate consonant. Whereas the semivowels y (IPA: j) and w tend also to be used as consonants, consonants such as ʾ and * show functional affinities with vowels (vowel).

Reconstructions based on Semitic and Cushitic alone point toward a balanced inventory of three short vowels (*i, *u, and *a) and three long vowels (*ii, *uu, and *aa). This, however, is unlikely to have been the case in the protolanguage; rather, in light of Chadic and Amazigh data and a more abstract level of phonological analysis, a two-vowel system (*a, *ə) appears more likely there.

Some phonemes, such as *y, *w, *ʾ, and *, appear to serve both as consonants (called “weak radicals” when they form part of a root) and as vowels (in which case they become *i, *u, and *a), depending on their distribution in the root or word. Conceivably, Proto-Afro-Asiatic lacked a vowel system in the traditional sense but may have distinguished consonants and sonants instead; examples of sonants would have been, for instance, *m, *n, *r, *l, *y, *w, *ʾ, *, and *^w, which could perform the functions of either consonants or vowels. As vowels they gave rise to *i, *u, and *a and sequences such as *am, *an, *ar, *al, *ai, *au, and *ʾa in the languages spoken today.

The majority of Afro-Asiatic languages are tone languages, meaning that in addition to consonants (consonant) and vowels (vowel), the pitch of the voice is used to differentiate between words or smaller meaningful units. The use of tones is attested in Chadic, Cushitic, and Omotic but in neither Semitic nor Amazigh. In some Cushitic and Omotic languages, however, tonality resembles pitch accent, a linguistic feature somewhat comparable to stress in European languages, albeit relying solely on higher pitch for “stressed” syllables rather than automatically combining higher pitch with loudness or duration. Some linguists believe that Proto-Afro-Asiatic was a tone language and that daughter languages such as Semitic, Amazigh, and possibly Egyptian subsequently lost all tonal distinctions. Other authors assume Proto-Afro-Asiatic was a pitch-accent language; these linguists consider it more likely that tonality emerged independently in Chadic, Cushitic, and Omotic, assuming that tonal distinctions, at least in Chadic, developed out of the pitch-accent system of Proto-Afro-Asiatic in conjunction with the pitch-lowering effect of certain syllable-initial consonants called tonal depressors. Such automatic pitch lowering is well attested outside Chadic both within and outside Africa. Thus, long periods of contact with speakers of genuine African tone languages of Niger-Congo and Nilo-Saharan stock may have assisted the historical shift from pitch accent to tone systems in Afro-Asiatic.

It is no coincidence that the West Semitic quasi-alphabets, which developed in the 2nd millennium BCE and from which all later Afro-Asiatic writing systems derive (including tifinagh of the Amazigh), are made up of signs that represent a consonant followed by any or no vowel, thus reflecting the structural properties of this characteristic root and pattern system.

The distinction of masculine and feminine genders (gender) in nouns and pronouns (in the second and third person, and both singular and plural) is maintained widely but has been lost in some subdivisions of Chadic and Omotic. In Semitic and Cushitic languages, a noun may change its gender when it changes from singular to plural, a feature known as “gender polarity.” For example, in the Cushitic language Burunge, kori ‘year' is a masculine noun, but korara ‘years' is feminine. Other languages use common gender in the plural (i.e., there is no gender distinction in the plural).

A notable historical feature is “gender stability,” meaning that words for common things tend to share the same gender across the languages of the Afro-Asiatic phylum, no matter whether or not the particular words are cognate across the specific languages in question. For instance, the word for “blood” is always masculine, although the forms of the word clearly have different origins: ahni in Tuareg (an Amazigh language), *bar in Proto-Chadic, boy in Beja (Cushitic), snf in Egyptian, and dam in Hebrew (Semitic).

Very similar pronouns are used in verb conjugation in both prefix and suffix position to indicate the person, gender, and number of the subject. For example, the third person singular feminine prefixes *ta- or *ti- can be found in Amazigh (t-dawa ‘she healed'), in the Chadic language Hausa (Hausa language) (tá-sàyáa ‘when she bought'), in the Cushitic language Bedawi (ti-dbíl ‘she collected'), and in the Semitic language Akkadian (Akkadian language) (ta-prus ‘she divided'). The corresponding suffix is found in conjugations in Amazigh (-t), Egyptian (-tj), and Semitic (*-at). Different but similar sets of suffixed pronouns are used to indicate object and possessor.

Other common elements can be found in noun derivation and inflection. A widespread element of derivation is *m-, used to derive agentive, locative, and instrumental nouns from verbs: compare the Arabic agentive mu-katib-un ‘the corresponding one' with the locative ma-ktab-un ‘the place to write' or ‘the school,' both of which are derived from the verb ‘to write.' Quite similar examples occur (for instance) in the Chadic language Hausa: má-hàif-íi ‘father (the begetting one),' má-háif-áa ‘birthplace, womb,' both of which are from the verb ‘to procreate, beget, give birth.'

Some Afro-Asiatic languages mark nouns for number in a manner quite different from that used in most Indo-European languages. Whereas English, for example, usually differentiates only between singular and plural, Classical Semitic and Egyptian routinely distinguished between singular, dual, and plural. This system has left traces in other divisions of Afro-Asiatic, which tend to have a rich array of plural marking devices. Some devices originate in the verbal system, where they mark plurality of action, actor, goal, or location. An example from the Chadic language Lamang is kəla ‘take,' kala ‘take many,' and kalala ‘take many here and there.' Noun plurals may be formed through the addition of affixes such as -uu or -w, and -n, which are particularly well attested, or through internal inflection. So, for example, in the Chadic language Hausa, “spear” is rendered máashìi while the plural form, máasúu, is created through a change in suffix. In contrast, the Amazigh for “wall,” agadir, becomes the plural form igudar through a change in internal inflection.

Together, the forms of pluralization combine to form “broken” plurals, such as in the Semitic language Geʿez, in which nəgus ‘king' becomes nägäs-t ‘kings.' Chadic and Cushitic languages also use repetition of final consonants, partly in combination with vowel changes, as in Hausa táfkìi ‘lake' and táfúkkàa ‘lakes,' and ḳáfàa ‘leg, foot' and its plural, ḳáfàafúu.

There are competing schools of thought surrounding the conjugational patterns of the protolanguage's verbal system. For decades heated debates have focused on the functions and interrelations of the most basic inflectional categories, often discussed in terms of dichotomous subsystems such as “state versus action,” “transitive versus intransitive,” “punctual versus durative,” or “perfective versus imperfective.” Likewise, there is considerable debate over the original marking devices for these categories and for the expressions of aspect, tense, and mood. Scholars have investigated the possibility that the protolanguage marked these categories through internal inflection in the root and pattern system, affixes, prefixal or suffixal person marking, and so on. Another question concerns which of these formations were actually nouns rather than verbs, or even something in between, such as participles or gerunds. A final area of discussion focuses on the relative age of certain recurring or missing features in the different divisions and languages.

Most scholars of Afro-Asiatic agree that the verbal systems of all Afro-Asiatic languages can ultimately be traced back to the common protolanguage (usually allowing for a unique development in Egyptian). However, the individual verbal systems have undergone considerable changes since then. Semitic and Amazigh, and to a lesser degree Cushitic, have maintained reflexes of the ancestral prefixal conjugation. This appears to have been largely lost in Chadic and Omotic and completely lost in Egyptian. The root and pattern system is well attested for Semitic, is less so for Amazigh, and is only rudimentary in Cushitic and Chadic.

Nominalized verb formations such as verbal nouns, participles, and predicative adjectives probably harken back to the protolanguage and can be reconstructed for predicates expressing state rather than action. This predicate form is commonly referred to as the “stative conjugation” and uses suffixes for indicating the person, number, and gender of the subject. Some conjugational paradigms of today's languages (and also of extinct ones such as Egyptian and Semitic Akkadian) derive from this suffix conjugation, including practically all paradigms in Egyptian, the Akkadian stative, the West Semitic perfective, and the qualitative in Kabyle (an Amazigh language). A greatly simplified analog of this conjugational form would be the English “eating-of-mine” for “I eat.”

Another common feature concerns the irregularity of imperative forms of the verbs “to come” and “to go.” These tend to use specific suppletive forms; that is, they replace the verb stem itself with another stem. Compare, for instance, the normal verb stem and the imperative form of “to come”: in Proto-Chadic these are *(-)sə and *ya, respectively; in Amazigh Kabyle as and eyya; in Egyptian nn and mn; and in Semitic Amharic mεṭṭä and na.

Afro-Asiatic verbs can be modified to indicate different kinds of qualities of action. Derivational extensions of verb stems (forming what are called “stirpes” or “themes”) use root modification (infixes) and derivative affixes together with partial or complete reduplication to indicate repeated action. Derivational markers may combine, which makes it possible for a single verb to indicate repeated action (by what is called the iterative derivation of the verb), action caused to happen (the causative derivation), action affecting the subject (the reflexive derivation), or action mutually affecting subject and object (the reciprocal derivation). The stirpes are commonly named after the affixed consonant. Thus, for the Proto-Semitic root *-p-r-s- ‘to divide,' the causative form is *-ša-p(a)ris (called the “S-stirps”), the reflexive is *-n-paris (the “N/M-stirps”), and the reciprocal is *-t-paris (the “T-stirps”).

Little historical work has been done on comparative Afro-Asiatic syntax; consequently, there is little agreement even on the original word order. Classical Semitic, Egyptian, and Amazigh all use a VSO (verb–subject–object) order, but almost all Cushitic languages use SOV order, and Chadic languages usually have SVO order. If, however, as Diakonoff suggested, Proto-Afro-Asiatic was an ergative type of language, in which subject and object as traditionally construed are not valid concepts, then such simple formulas would not be at all useful in explaining the syntax of the protolanguage.