Use of reflexive?
Why is me, te, se, nos used before a verb in a seemingly non-reflexive context at times? What are the rules? Sometimes I see sentences like this one: Se comió la cena en mi casa. I have also seen it like this: Comió la cena en mi casa. Both appear to mean, He/she ate supper at my house. I understand the concept of the reflexive, the idea of doing the action of the verb to yourself. But sometimes, like here, it looks like the reflexive is used but I cannot understand why.
2 Answers
Se in your example is not reflexive but indicates a quality of the action:
Se comió la cena ...... He / she ate up the supper (the whole meal).
Comió la cena ..... He / she ate the supper (maybe not all of it / maybe slowly).
Reflexive: Ella se peinó ..... She combed her hair.
Not reflexive: Ella me envió una carta .... She sent me a letter (the personal pronoun here indicates who is affected by the action, the indirect object).
Not reflexive: Se me cayó la cartera .... I dropped my wallet / my wallet fell from my hand (Se here indicates sudden action / me is who is affected by this action).
Here is a review of se from the old reference section here, some of these are specific to se, but some include uses in your question, and I thought this might be of additional help in addition to the excellent answer by Julian :
Transitive and intransitive constructions: use of "se" (by Lazarus) 20
The most conservative classifications give SE 6 different uses; the most standard ones 7-8, and other more detail ones over 10 uses. More or less:
1) When you get any the 8 combinations 'le(s) lo(s)' or 'le(s) la(s)', with indirect and direct object pronouns before the verb, 'le(s)' changes to SE, always.
2) SE can be a reflexive direct object pronoun: Yo me lavo y él se lave (I wash myself and he washes himself). It can also be a reflexive indirect object: Te limpio el zapato y se limpia el zapato (... he washes his own shoe)
3) SE can be a reciprocal pronoun: Se aman (they love each other).
4) SE can be used for impersonal constructions. The verb is always in 3rd person singular, and there is no grammatical subject, but there can be objects: Se recibe a los invitados.
5) SE can be used for 'passive reflexive' constructions. The verb can only be in 3rd person, and it must agree in number with the subject, which is normally placed after it: Se vende esta casa. Se venden estas casas. (these houses are sold)
6) SE is sometimes an essential part of some verbs that cannot function without it, and does not even appear in the dictionary without the pronoun: Me arrepiento.
7) With many transitive verbs, it makes them intransitive, often eliminating the cause or agent that provoked the action: Rompo la radio (I break the radio). La radio se rompió (the radio broke). Lo enfadé (I annoyed him). Me enfadé (I got annoyed).
8) With some intransitive verbs, such as 'ir' or 'caer', it places special focus on the beginning of the action, or whatever caused the change. 'Ir' requires a destination, like 'to go (to a place)'; 'irse' doesn't, like 'to leave'.
9) Many transitive verbs take a SE that delimits the action, sometimes modifying the meaning of the verb. Most well known examples are verbs of consumption, like 'comer', 'beber', 'fumar',... 'Comer' is one of the few ones that sometimes requires this 'SE'; in all other verbs it is similar to the difference between 'wash' and 'wash up', and suppressing them does no harm.
