Indo-European copula
A feature common to all Indo-European languages is the presence of a verb corresponding to the English verb "to be". General features. This verb has two basic meanings: Some languages have shared these functions between several verbs: Irish, Spanish and Persian all have multiple equivalents of "to be", making a variety of distinctions. Many Indo-European languages also use the conjugations of the verb "to be" as an auxiliary for the formation of compound (periphrastic) tenses ("I’m working"; "I was bitten"). Other functions vary from language to language. For example, although in its basic meanings , "to be" is a stative verb, English puts it to work as a dynamic verb in fixed collocations ("You are being very annoying"). The copula is the most irregular verb in many Indo-European languages. This is partly because it is more frequently used than any other, and partly because Proto-Indo-European offered more than one verb suitable for use in these functions, with the result that the daughter languages, in different ways, have tended to form suppletive verb paradigms. This article describes the way in which the irregular forms have developed from a series of roots. The Proto -Indo-European [PIE] roots. Section::::"*hes-". The root "*hes-" was certainly already a copula in Proto-Indo-European. The e-grade "*hes-" (see Indo-European ablaut) is found in such forms as English "is", Irish "is", German "ist", Latin "est", Sanskrit "asti", Persian "ast," Old Church Slavonic "ѥстъ (jestŭ)". The zero grade "*hs-" produces forms beginning with /s/, like German "sind", Latin "sumus", Vedic Sanskrit "smas", etc. In PIE, "*hes-" was an athematic verb in "-mi"; that is, the first person singular was "*hesmi"; this inflection survives in English "am", Pashto "yem", Persian "am", Sanskrit "asmi", Bengali first-person verb ending  -ām, Old Church Slavonic ("esmĭ"), etc. This verb is generally reconstructed for Proto-Indo-European thus: The root or (which did not have ablaut variations in the protolanguage) probably meant 'to grow', but also 'to become'. This is the source of the English infinitive "be" and participle "been". Also, for example, the Scottish Gaelic "future" tense "bithidh"; the Irish imperative "bí", past "bhí" and future "beidh"; the Welsh (along with the other "b-" initial forms); Persian imperative "bov", past "bud" and future "bâš"; and the Slavic infinitive, etc. for example Russian ("byt’"). PIE became Latin /f/, hence the Latin future  participle "futūrus" and perfect "fuī"; Latin "fīō" 'I become' is also from this root, as is the Greek verb ("phúō"), from which "physics" and "physical" are derived. This verb can be reconstructed as follows: Section::::"*hwes-". The root "*hwes-" may originally have meant "to live", and has been productive in all Germanic languages. The e-grade is present in the German participle "gewesen", the o-grade ("*wos-") survives in English and Old High German "was", while the lengthened e-grade ("*wēs-") gives us English "were". (The Germanic forms with /r/ result from grammatischer Wechsel.) See Germanic strong verb: Class 5. Section::::"*her- . This has been claimed as the origin of the Old Norse and later Scandinavian languages' present stem: Old Norse em, ert, er, erum, eruð, eru"; the second person forms of which were borrowed into English as "art" and "are". It has also been seen as the origin of the Latin imperfect ("eram, eras, erat") and future tenses ("ero, eris, erit"). However, other authorities link these forms with "*hes-" and assume grammatischer Wechsel (/s/→/r/), although this is not normally found in the present stem. Donald Ringe argues that the copula was sometimes unaccented in Pre-Proto-Germanic, which would have then  triggered the voicing under Verner's law. He explains the Germanic first person singular form as such, deriving it from earlier , since -zm-, but not -sm-, was assimilated to -mm- in Germanic (for which other evidence exists as well). Furthermore, the third person plural form (from PIE ) shows that this word, too, was unaccented. If the accent had been preserved, it would have become , but that form is not found in any Germanic language. In this view, it is likely that stressed and unstressed varieties of the copula (with corresponding voiceless and voiced fricatives) existed side by side in Germanic , and the involvement of a separate root "" is unnecessary. The Latin forms could be explained by rhotacism. Section::::"*steh-". The root "*(s)teh-" meant "to stand". From this root comes the present stem of the so-called "substantive verb" in Irish and Scottish Gaelic, "tá" and "tha" respectively, as well as "taw" in Welsh. On the absence of the initial s- in Celtic, see Indo-European s-mobile. In Latin, "stō, stare" retained the meaning "to stand", until local forms of Vulgar Latin began to use it as a copula in certain circumstances. Today, this survives in that several Romance languages (Galician -Portuguese, Spanish, Catalan) use it as one of their two copulae, and there is also a Romance tendency for a past participle derived from "*steh-" to replace the original one of the copula (this occurs in French, Italian and the main dialects of Catalan). See also Romance copula. German "stehen" also exhibits a similar secondary meaning as a copula in certain locative phrases. For example, "Das Auto steht da" ("the car is over there" lit. "the car stands there"). Although in Dutch, this verb retains its primary meaning of "stand", it is also used in an auxiliary-like function that  only has a secondary meaning of "standing", for example: "ik sta te koken" ("I am cooking", literally "I stand to cook"). When it is not a full copula (it can normally only be used as an auxiliary with another verb), it does have shades of meaning that resemble that of the Italian "sto cucinando" ("I am cooking"). The intransitive verbs "zitten" ("to sit"), "liggen" ("to lie") and "lopen" ("to walk/run") are used in similar ways. In Swedish, which usually lacks gerund forms, the corresponding "stå" is often used similarly, along with "sitta" ("to sit"), "ligga" ("to lie") and "gå  (to walk"). In Hindustani the past tense of the copula "honā" "to be" which are «tʰā», «tʰe», «tʰī» and «tʰī̃» are derived from Sanskrit «stʰā». Gujarati has a cognate verb «tʰavũ» "to happen"; cf. Bengali aorist «tʰā-» (to stay) as well. The resulting paradigms. Indo-Iranian languages. Indic languages. Sanskrit. The Vedic Sanskrit root "as" (to be) is derived from the Indo-European root *"". "bhū" (to be) is derived from Indo-European *"". Hindi-Urdu. In modern Hindi-Urdu (Hindustani), the Sanskrit verb अस् "(as)" (to be) which is derived from the Indo-European root "* has developed into the present indicative  forms of the verb होना ہونا "(honā)" (to be). The infinitive होना ہونا "(honā)" itself is derived from the Sanskrit verb root भू "(bʱū)" which is derived from Indo-European root *." The indicative imperfect forms of होना ہونا "(honā)" comes from Sanskrit स्थित "(stʰita)" "standing, situated" which are derived from the PIE root *steh₂- (“to stand”). होना ہونا (honā) is the only verb in Hindi-Urdu to have the "present indicative", "imperfect indicative", "presumptive mood" and the "present subjunctive" conjugations, and all the other verbs in Hindi-Urdu lack them. The verb होना / ہونا (honā) can be translated as "to  be", "to exist", "to happen" or "to have" depending on the context, and when used in the third person it could also be translated as ""there is/are"". Many verbs conjugations in Hindi-Urdu are derived from participles and hence are gendered and numbered, and they agree with either the object or the subject of the sentence depending on the grammatical case of the subject of the sentence. When the subject is in the ergative or the dative case (seeː dative construction & quirky subject) the verb agrees in gender and number with the object of the sentence and with the  subject when the subject is in the nominative case. Bengali. Bengali is considered a zero copula language, however there are notable exceptions. In the simple present tense there is no verb connecting the subject to the predicative (the "zero verb" copula) but when the predicate expresses ideas of existence, location, or possession, for such cases the verb আছ- ("ach") can be roughly translated as "to exist" or "to be present". Bengali verbs are highly inflected and are regular with only few exceptions. They consist of a stem and an ending; they are traditionally listed in Bengali dictionaries in their "verbal  noun" form, which is usually formed by adding "-a" to the stem: for instance, করা ("kôra, to do") is formed from the stem কর ("kôr"). The stem can end in either a vowel or a consonant. Nepali. The copula verb of Nepali has two sets of conjugations. The हो (ho) set is used in sentences that equate two things, like त्यो किताब हो (tyo kitāb ho, “That is a book.”) The छ (cha) set is used in sentences that describe something, or locate where something is, like त्यो ठूलो छ (tyo ṭhūlo cha, “That is big.”). Singular present tense forms  of the copulas in Nepali are shown in the table below: Iranic languages. Persian. With regard to the function of the verb ‘to be’ as a copula, the most conspicuous feature of Modern Persian language is the evolution of an "existential be", hast (exists), out of ast (is). In fact, when studying the forms and functions of ‘to be’, one might find certain characteristics specific to Persian that is worth pondering upon— i.e. even without considering the diachronic evolution of Modern Persian language and its relation to Ancient Iranian languages (such as Old Persian and Avestan) whose usage of the  verb ‘to be’ seems more close to Sanskrit. Paradoxically, despite the fact that Persian is apparently the only Indo-European language that has created an "existential be" out of the copula, it has simultaneously made an extreme use of the latter to produce a general paradigm for conjugating all Persian verbs. Historically speaking, like most of Indo-European languages that make use of suppletive roots to denote ‘to be’, Persian integrates Proto-Indo-European (PIE) verbs *hes- (to be) and *buH (to grow> to become> to be). Hence, while Persian infinitive būdan (to be) < PIE "*buH" forms  the past stem of the verb (e.g. Persian būd- ‘was’) or acts as an auxiliary verb in formation of pluperfect of other verbs, its present tense is solely based on the derivatives of PIE *"hes-. It is, in fact, from the declension of PIE *"hes- (to be) that six present stems have been created and assigned to the 1st, 2nd, and 3rd person singular and plural to act as the present-tense conjugation of Persian būdan (to be), as shown in the following table. As an example, in the following sentences, the present forms of the verb 'to be' are  used as copulas or predicates: Furthermore, as endings added to the stem of the verbs, these declensional forms have been grammaticalized to shape a general paradigm for the grammatical conjugation of all other verbs; these endings were once auxiliary verbs which evolved into an enclitic. This generalized conjugational paradigm is also applied to the past tense of the verb "būdan" (shown in the table below). However, what is linguistically notable, is the emergence of an "existential be" out of the "copula", viz hast (exists) out of ast (is). The evolution of this exceptional form, might go back to ancient Iranian  languages, where ast could have two variants (cf. Avestan which has both as- and has- <PIE *hes- ‘be’). In the next phase, what we may call a "pseudo-verb appeared, vis. the verb hastan (to exist) has been "analogically" evolved from hast (exists) and has been conjugated like any other Persian verb (e.g. "hast-am = literally: *‘"(I) am existence"’→ ‘I exist’). The simple past conjugation of the verb būdan (to be) is in fact formed by a double-copula, in the sense that both the stem and the ending are copulas: the past stem of the verb "būd"-  is derived from PIE *buH-, while the endings are from the suppletive form of PIE *hes- (to be) with the exception of 3rd person singular which has zero ending for the all Persian verbs in the past tense. The present perfect conjugation of the verb būdan (to be) is a double copula paradigm as it is produced by addition of all enclitic copulas to the past participle of the verb: būde (been). The pseudo-verb hastan (to exist) has only simple present tense; in addition, it is truly and purely existencial only in the case of third person singular (hast ). The fact is that the verb has been the product of this very case, as an "existential is", hast (he/she/it exists). For other persons the conjugation has to use enclitic copulas. These copulas are, in turn, derived from the declension of PIE *hes- (to be); as if the predicative "to be" has been an auxiliary verb turned into enclitic, to provide six endings for 1st/2nd/3rd person (singular & plural). However, as it is said, the 3rd person singular has no ending in the case of hastan. That is to say that the existential hast (exists), which is like the  alter-ego of the copula ast (is), takes no ending, while the present stem of all other verbs take an archaic ending -"ad" in their 3rd person singular. Hellenic languages. Greek. The Ancient Greek verb "eimi" (I am) is derived from the Indo-European root *"". The participles are based on the full-grade stem ἐσ- in Homeric, according to Smyth. Italic languages. Except for Latin, the older Italic languages are very scarcely attested, but we have in Oscan "set" (they are), "fiiet" (they become), "fufans" (they have been) and "fust" (he will be), and in Umbrian "sent" (they are). This  section will explain Latin, and the Romance languages that have evolved from it. "Esse" and the forms beginning with (e)s- are from the root "*hes-", while the forms beginning with "f-" are from the root . For the forms beginning with er-, see "". "Stāre" is derived from the root "*steh-". In Spanish, Catalan, Galician-Portuguese and to a lesser extent, Italian there are two parallel paradigms, "ser/èsser/essere" from Latin "esse" "to be" on the one hand, and "estar/stare" from Latin "stare", "to stand" on the other. In several modern Romance languages, the perfect is a compound tense formed  with the past participle as in English, but the old Latin perfect survives as a commonly used preterite in Spanish and Portuguese, and as a literary "past historic" in French, Italian and Catalan. There is a tendency for a past participle derived from "stare" (or more specifically its supine, "statum") to replace that of the main copula derived from "esse". For example, the French participle "été" comes from "statum". Germanic languages. Proto-Germanic retained the dual, but only in the first and second person. Baltic languages. In Lithuanian, the paradigm "būnu, būni, būna", etc. is not considered archaic or dialectal  but rather a special use of the verb "būti", to be, mostly used to describe repeated actions or states, or habits. Celtic languages. In the Celtic languages there is a distinction between the so-called substantive verb, used when the predicate is an adjective phrase or prepositional phrase, and the so-called copula, used when the predicate is a noun. The conjugation of the Old Irish and Middle Welsh verbs is as follows: The forms of the Old Irish present tense of the substantive verb, as well as Welsh "taw", come from the PIE root *"stā-". The other forms are  from the roots *"es-" and *"bhū-". Welsh "mae" originally meant "here is" (cf. "yma" 'here'). Irish and Scottish Gaelic. In modern Gaelic, person inflections have almost disappeared, but the negative and interrogative are marked by distinctive forms. In Irish, particularly in the south, person inflections are still very common for the "tá/bhí" series. The copula. Gaelic "(bh)eil" and Irish "(bh)fuil" are from Old Irish "fuil", originally an imperative meaning "see!" (PIE root "*wel-", also in Welsh "gweled", Germanic "wlitu-" "appearance", and Latin voltus "face"), then coming to mean "here is" (cf. French "voici < vois ci" and "voilà <  vois là"), later becoming a suppletive dependent form of "at-tá". Gaelic "robh" and Modern Irish "raibh" are from the perfective particle "ro" ("ry" in Welsh) plus "ba" (lenited after "ro"). Modern Welsh. The present tense in particular shows a split between the North and the South. Though the situation is undoubtedly more complicated, King (2003) notes the following variations in the present tense as spoken (not as written according to the standard orthography): For example, the spoken first person singular dw i'n is a contraction of the formal written yr ydwyf fi yn . The Welsh F /v/ is the  fricative analogue of the nasal /m/, the PIE suffix consonant for the first person singular. Hittite. The Hittite verb "to be" is derived from the Indo-European root *". Armenian. The Classical Armenian present tense derives from PIE *'- (cf. sg. ', ', '; 3rd pl. "). Albanian. The Albanian copula shows two distinct roots. The present "jam" ‘I am’ is an athematic root stem built from PIE *'. The imperfect continues the PIE imperfect of the same root but was rebuilt based on the 3rd person singular and plural. The preterite, on the other hand, comes from the thematic aorist of PIE *' ‘turn’ (cf. Ancient Greek  épleto ‘he turned’, Armenian "eɫew" ‘he became’, Old Irish "cloïd" ‘turns back, defeats’). Analogical or otherwise indirect reflexes are italicized below.