Haber (to have)

is used as an auxiliary verb to form compound tenses of other verbs. It is generally followed by a past participle. The present tense combined with a past participle forms the perfect tense. The imperfect combined with a past participle forms the pluperfect tense.

	present	imperfect
yo	he	había
tu	has	habías
él	ha	había
nosotros	hemos	habíamos
vosotros	habéis	habíais
ellos	han	habían

Examples:

Yo he comprado un libro. - I have bought a book.

Vd. no ha escrito la carta. - You have not written the letter.

Note that the negative no precedes the auxiliary.

he hallado - I found

había hallado - I had found