Preposition and direct objects which are persons

Question

I made several mistakes regarding prepositions in a Spanish text, and my teacher wrote this at the end:

Un caso específico de preposiciones que faltan es cuando se trata de un objeto directo que es una persona.

There was also an exhortation to look it up in a grammar book. However I can't find it in my grammar book. Can anyone explain what this rule means? What is it that I need to know about prepositions in front of direct objects which happen to be persons?

Answer 1

As a rule, indirect objects must be preceeded with either a or para.¹. Also as a rule, direct objects (like subjects) are bare. That means they can be quickly identified in sentences because they have no preposition introducing them.

Direct objects have two exceptions, though:

1. If the direct object is anthropomorphized (a person, or something we see as a person, e.g., a pet), then you must place an a in front of it. This is very common.
2. If the direct object could be otherwised confused for the subject, then you may/ought to place an a in front of it to make it clear it is not the subject: Come el lobo el zorro could use an a to let us know which animal was eaten. Comen los lobos el zorro does not, because there is no ambiguity.

As you can see, the first exception is what is getting at you. Always, 100% of the time, if your direct object is a person (or pet), use a for direct objects. You can actually simplify this to, regardless the object, just use a if it's a person (because indirect objects can also take a).

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^{1. There is a difference between these two: a allows redudancy with object pronouns (di algo a Juan or le di algo a Juan) and in fact requires it when the explicit indirect object is a pronoun itself (like mí, ti, él, ella, etc). Quite differently, para categorically rejects the redudancy (only di algo para Juan) such that when para is seen with an indirect object pronoun (as in le di algo para Juan), the indirect object pronoun indicates a third person, and the para clause is a sort of obviative — effectively, a fourth person.}

Answer 2

Could you give us an example of a sentence where your teacher's suggestion applies? I'm spanish and I cannot figure out what your teacher means...

UPDATE:

Ok, now I see; when a person receives the benefit or damage (beneficio o daño in spanish) of an action (which is called the Indirect Object IC, or Dativ in German), a preposition is required, to indicate who is the target of the action. In your examples, "las criaturas" (the beings), "todos" (all) are the "actors" or the "targets" of the action. They could be human beings, animals or whichever target personified:

El cazador mató al pájaro de un sólo tiro.

Remember that "al" is a contraction of the preposition a + the singular, masculine article el.

El chico explicó a su padre lo que había ocurrido.

Some verbs require only Direct Complement (DC). DC may be things-DC:

Él vio la pared.

or persons-DC.

Él vio a Laura.

The same applies, as you can see. When a person is involved in a Direct Complement or Indirect Complement a preposition ("a" in case of DC, "a" or "para" in case of IC) is required.

Llevo estas flores para Ana.

I hope this helps.