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A copula is a word that links the subject of a sentence with a predicate (a subject complement). In English, the copula is the verb "to be" (for example, the word "is" in the sentence "The sky is blue.")

Most languages have one main copula, but some, such as Spanish, Portuguese and some other Romance languages, have more than one. This is because the verb or verbs meaning "to be" in the Romance languages are derived from not just one but three Latin verbs:

As the Romance languages developed over time, the three separate Latin verbs became just one or two verbs in the Romance languages.

The reduction of three separate verbs into just one or two happened in the following ways:

The development of two copular verbs in this manner occurred most completely in Spanish, Portuguese and Catalan. In other languages, most usages of English "to be" are still translated by *essere:

Portuguese also developed an additional copular verb ficar, with the meaning "to be located" and "to become."

In English, it is possible to say "there stands..." instead of "there is..." in certain contexts. In Latin, too, it became common to eschew SVM in favour of STO and say where things "stood" instead of where they "were". With time, it became common to use this verb to express other states.

Today, Spanish, Galician, Portuguese, Catalan, and (to a lesser extent) Italian commonly use two copulas, one from each of the Latin verbs. The others use just one main copula, from SVM.

There is also a notable tendency for a derivative of the supine of STO (STATVS, STATA, STATVM) to replace the past participle of verbs deriving from SVM (which in Latin had no supine). Examples:

The Spanish copulas are ser and estar. The latter developed as follows:

The copula ser developed from two Latin verbs. Thus its inflectional paradigm is a combination: most of it derives from SVM (to be) but the present subjunctive appears to come from SEDEO (to sit) via the Old Spanish verb seer.

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