Persian and Armenian are the only agglutinative Indo-European languages.
Persian is the only agglutinative Iranian language.
An agglutinative language is a language that uses agglutination extensively: most words are formed by joining morphemes together. This term was introduced by Wilhelm von Humboldt in 1836 to classify languages from a morphological point of view. It is derived from the Latin verb agglutinare, which means “to glue together”.
In agglutinative languages, each affix typically represents one unit of meaning (such as “diminutive”, “past tense”, “plural”, etc.), and bound morphemes are expressed by affixes (and not by internal changes of the root of the word, or changes in stress or tone). Additionally, and most importantly, in an agglutinative language affixes do not become fused with others, and do not change form conditioned by others.
Synthetic languages that are not agglutinative are called fusional languages; they sometimes combine affixes by “squeezing” them together, often changing them drastically in the process, and joining several meanings in one affix (for example, in the Spanish word comí “I ate”, the suffix -í carries the meanings of indicative mood, active voice, past tense, first person singular subject and perfective aspect).
Agglutinative is sometimes used as a synonym for synthetic, although it technically is not. When used in this way, the word embraces fusional languages and inflected languages in general.
The distinction between an agglutinative and a fusional language is often not sharp. Rather, one should think of these as two ends of a continuum, with various languages falling more toward one end or the other. For example, Japanese is generally agglutinative, but expresses fusion in otōto (弟 younger brother?), from oto+hito (originally oto+pito). In fact, a synthetic language may present agglutinative features in its open lexicon but not in its case system (e.g. German, Dutch, and Persian).
Agglutinative languages tend to have a high rate of affixes/morphemes per word, and to be very regular, in particular with very few irregular verbs. For example, Japanese has very few irregular verbs – only two are significantly irregular, and there are only about a dozen others, with only minor irregularity; Ganda has only one (or two, depending on how “irregular” is defined); Turkish has only one and in the Quechua languages all the verbs are regular. Korean language has only ten irregular forms of conjugation. Georgian is an exception; not only is it highly agglutinative (there can be simultaneously up to 8 morphemes per word), but there are also a significant number of irregular verbs, varying in degrees of irregularity
A fusional language (also called inflecting language) is a type of synthetic language, distinguished from agglutinative languages by its tendency to overlay many morphemes to denote grammatical, syntactic or semantic change.
Examples of fusional Indo-European languages are Sanskrit (and the modern Indo-Aryan languages), Greek (classical and modern), Latin, Lithuanian, Russian, German, Icelandic, Polish, Croatian, Serbian, Slovak, Ukrainian and Czech. Another notable group of fusional languages is the Semitic languages group. A high degree of fusion is also found in many Sami languages, such as Skolt Sami.
An illustration of fusionality is the Latin word bonus “good”. The ending -us denotes masculine gender, nominative case, and singular number. Changing any one of these features requires replacing the suffix -us with a different one. In the form bonum, the ending -um denotes either masculine accusative singular, neuter accusative singular or neuter nominative singular.
Fusional languages are generally believed to have descended from agglutinative languages, though there is no linguistic evidence in the form of attested language changes to confirm this view. On the other hand, fusional languages generally tend to lose their inflection over the centuries—some languages much more quickly than others.
For example, while most Uralic languages are predominantly agglutinative, Estonian is markedly evolving in the direction of a fusional language. On the other hand, Finnish, its close relative, exhibits fewer fusional traits, thereby keeping closer to the mainstream Uralic type.
Also, supposedly, Sanskrit, Latin, Slovenian, Lithuanian, and Armenian are about as fusional as the unattested Proto-Indo-European, but modern English and Afrikaans are almost entirely analytic. The Slavic and Baltic languages have generally retained their inflection, along with Greek.
These characteristics reflect many of the features of the extinct languages that were spoken within the region, until recently known as the Armenian Plateau (currently designated as Anatolia) and its immediate surroundings.
The Hurro-Urartian languages (circa 2000-580 BC) were agglutinative languages, but they definitely did not belong to the Semitic or Indo-European language families. Scholars such as I.M. Diakanoff and Segei Starostin see affinities between Hurro-Urartian and the Northern Caucasian languages, yet, there is little evidence for a relationship of Hurro-Urartian to other language families and this view, prudently, is not shared by serious linguists who consider Hurro-Urartian as an independent family at present.
Today, studies demonstrate that there is evidence of a strong Hurrian cultural and linguistic influence on Hittite in ancient times. Consequently, one can easily conclude that together with Summerian, Elamite, Hattic or Urartian languages, Armenian grammar inherited some of its grammatical and lexical elements from the languages that have seen their political and military rise and fall throughout the ages. Astoundingly, Armenian language seems to be the only survivor as well as the only link to these extinct languages and civilizations.