Indo-European copula copula (with corresponding voiceless and voiced fricatives) existed side by side in Germanic, and the involvement of a separate root "" is unnecessary. 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. 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
Indo-European s-mobile Indo-European s-mobile In Indo-European studies, the term s-"mobile" (; the word is a Latin neuter adjective) designates the phenomenon where a PIE root appears to begin with an "" which is sometimes but not always present. It is therefore represented in the reflex of the root in some attested derivatives but not others. This "movable" prefix "s-" appears at the beginning of some Indo-European roots, but is absent from other occurrences of the same root. For example, the stem "", perhaps 'bison', gives Latin "taurus" and Old English "steor" (Modern English "steer"), both meaning 'bull'. Both variants existed side by