Language/Spanish/Grammar/Use-the-letters-V-and-B

All words in which this letter goes before another consonant are written with "b"

Examples: libro, amable, subterráneo, obsequio.

Before "m" and "p" is written "b", and after "n", "d" and "b" write "v"

Examples: embajador, empezar, enviar, adversario, subvención.

Words that begin or end with "bio" are written with "b"

Examples: biografía, biología, anfibio.

Words ending with "bilidad" are written with "b", except: "movilidad" - "civilidad"

Examples: responsabilidad, amabilidad.

They are written with "b" the terminations of the past imperfect indicative of the verbs of the 1st conjugation and also preterite imperfect indicative of the verb "ir"

Examples: amábamos, cantabáis, alzaba, iba, ibas, íbamos.

All the compound words of the verb "venir" are written with "v"

Examples: convenir, prevenir.