Spanish Miscellaneous

Passive Voice in Spanish

Generally we use the passive voice to indicate what happened to the subject of the sentence without saying who or what carried out the action, meaning that in the passive voice (voz pasiva), the subject is acted upon by an outside agent. When the agent is specified, the passive voice is expressed by:
subject + ser + past participle + por + agent: for example: La mezquita fue construida por el Sultán Hassan (The mosque was built by the Sultan Hassan).
From active to passive voice: Mis amigos quieren a mi perro becomes Mi perro es querido por mis amigos.

Since the past participle acts as an adjective, it agrees in gender and number with the subject. If the passive subject is a thing and the agent is not mentioned, the passive reflexive (pasiva reflexiva) construction is used, with the reflexive pronoun se preceding the verb and the passive subject following it:
Allí se hablan muchos idiomas (many languages are spoken there). No se permite hacer modificaciones (making modifications is not allowed).

Note that the Spanish past participle has to agree with the subject in gender and number, just the way it does withadjectives
Impersonal Constructions in Spanish

Se is also used to form impersonal construction, with se used as an indefinite subject pronoun in Spanish similar to the English "one" or the impersonal "you" and "they", like: Se habla español (Spanish is spoken / One speaks Spanish). There are two main criteria to be met: the verb must be in the singular, since se is singular when used as a subject pronoun, and se should be easily translated as one or you:

Participles and Progressive Tenses in Spanish

Gerund in Spanish

The present participle or gerund (gerundio) is formed in Spanish by adding the suffix -ando to the stem of the first conjugation (-ar) verbs and -iendo to the stem of second (-er) and third (-ir) conjugation verbs (or -yendo if the stem ends in a vowel).
hablar (to talk) hablando (talking)
comer (to eat) comiendo (eating)
vivir (to live) viviendo (living)
leer (to read) leyendo (reading)
The present participle is used with the verb estar to form the progressive tenses (tiempos progresivos), which express an ongoing action: Estoy hablando con ellos (I’m talking to them) Estaba leyendo el libro (he was reading the book). The same construction is used with seguir and continuar: Sigue peleando (he keeps fighting); Continuan riendo (They continue laughing). The present participle is also used with the verb ir to express an action which is gradual: La economía China Va Mejorando (Chinese economy is getting better).

Note that the progressive construction is never used for estar, venir and ir.

Past Participle in Spanish

The past participle (participio pasivo) is formed in Spanish by adding the suffix -ado to the stem of -ar verbs, and -ido to the stem of -er and -ir verbs (or -ído if the stem ends in a vowel).
hablar (to speak) hablado (spoken) becomes el español hablado en canarias…(the Spanish spoken in the canaries island…)

perder (to lose) perdido (lost) la chica perdida (the lost girl)
incluir (to include) incluido (included) el desayuno está incluido en el precio (breakfast is included in the price)
caer (to fall) caído (fallen) caído del cielo (fallen from the sky)
When used with the auxiliary verb haber to form compound tenses, the past participle has an invariable ending:
Hemos cerrado la escuela. (We have closed the school.)
Habrá perdido el pasaporte. (He will have lost the passport.)
Habías recibido un regalo. (You had received a gift.)
Entraron después de que hubo caído. (They entered after he had fallen down.)

When used adjectivally, however, Spanish past participles agree in gender and number with the nouns they modify:
La escuela está cerrada. (The school is closed.)
Las chicas están perdidas. (The girls are lost.)