The Vulgar Latin spoken by Roman armies and settlers in ancient Spain formed the basis of the many Spanish dialects that developed in the various regions of the country during the Middle Ages. The dialect of Castile, or Castilian Spanish, gradually became the accepted standard as Castile gained political dominance in the 13th century.
In its grammatical structure Spanish is generally in conformity with French, Italian, Portuguese, and the other Romance languages. A pronounced peculiarity of Spanish grammar, however, is the use of the preposition a (normally meaning "to") as an untranslatable particle before the direct object of a verb if that object is a person; for example, veo a mi amigo ("I see [particle] my friend"). The four conjugations of Latin have been reduced in Spanish to three; furthermore, regular verbs of the Spanish second and third conjugations differ in only four forms, namely, the present infinitive, the first and second persons plural of the present indicative mood, and the second person plural of the imperative mood.
The subjunctive mood persists in Spanish with much greater vigor than in most modern languages, having, besides the customary present and imperfect tenses, a second imperfect form derived from the Latin pluperfect indicative. Auxiliaries are used to form the compound tenses, as in the other Romance languages; for the perfect tenses, the auxiliary in Spanish is always a form of haber ("to have"), while in French and Italian, in contrast, "to be" is used for the perfect of certain verbs. Spanish far exceeds most of the other Romance languages in its idiomatic use of reflexive verbs with special meanings. As in the other Romance tongues, the Spanish future and conditional indicative are really compounds formed by adding to the entire infinitive (used as a stem) the present and imperfect indicative endings, respectively, of haber. The Spanish neuter gender survives in a few instances: in the singular of the definite article lo, in the demonstrative words esto, eso, and aquello, and in the third-person objective pronoun lo. These neuter forms occur only in indefinite and general constructions and in those in which the neuter article, accompanied by an adjective or adverb, forms abstract expressions; thus, lo bueno, "the good," means "goodness."
While the majority of Spanish words derive from Latin, many are taken from other sources; for example, pre-Indo-European languages such as Iberian, Basque, and also from Indo-European Celtiberian. The invasion of the Visigoths early in the 5th century AD introduced a few Germanic words. The Muslim conquest three centuries later brought in a large number of Arabic words, many of which are easily detected by the prefixed Arabic article al. Under the influence, beginning in the 11th century, of French ecclesiastics and pilgrims on their way to Santiago de Compostela in northwestern Spain, the Spanish vocabulary was appreciably augmented by words and phrases from French. During the 15th and 16th centuries an infusion of elements from the Italian occurred because of Aragonese domination in Italy and the great vogue of Italian poetry in Spain. Relations between Spain and its colonies and possessions have led to the introduction of terms from Native American languages and other sources, and scholarly activities have constantly increased the stock of borrowed words.