Hay… and More
The verb haber lives a double life. On the one hand, it can be a helping verb (also known as an auxiliary verb) that is used in all persons and numbers, tenses and moods to form the perfect tenses. On the other, it exists only in the third-person singular — in all tenses and moods, as an impersonal verb, also often referred to as an existential verb.
In the present tense, this form is not the same as the form it uses when the third person singular is used to form the present perfect, e.g. Él ha comido. Instead, it is hay, meaning both there is and there are. Some learners, even at the intermediate level, still confuse the use of this verb with the functions of ser and estar. The difference can be shown easily with a couple of examples. If one wishes to say John is a man, the statement is personal and hay cannot be used, i.e., Juan es hombre. Likewise, if we want to say that John is here, we say Juan está aquí. These are personal statements, not impersonal ones. But if we see a man on the corner, we can say Hay un hombre en la esquina; if there are two or more men, we can say Hay muchos hombres en la esquina. These types of statements do not treat the man or men in a personal way.
When to Use It
Most learners overcome the temptation to use ser or estar when they should use hay by remembering that, quite simply, if English would employ there is or there are, you resort to hay. This reassurance breaks down when they learn past tenses, however, particularly with regard to ser and estar. So, the next thing learners need to remember is that the third-person singular forms of the verb haber in all tenses are also impersonal or existential. For instance, there was or there were is rendered by the imperfect or preterite of haber: había or hubo; there would be is habría and there will be is habrá.
The third-person singular of haber in its two subjunctive tenses are also used as impersonals: Dudo que haya alguien en el restaurante a estas horas (I doubt there is anyone in the restaurant at this hour) or No creía que hubiera nadie en el restaurante (I didn’t believe there would be/there was anyone in the restaurant).
By memorizing these few examples, you can avoid most of the confusion about the uses of these verbs — and expand your command of natural-sounding Spanish.