Usage of "se"

Question

I have searched through the forums for the usage of "se", but I am still not satisfied. I notice "se" is pretty much littered everywhere in Spanish, I know some basic usages(indirect pronoun, impersonal, passive), but I am still confused as to when I should add a "se"....Any tips for using it would be great

Here are some examples

Se me caen las llaves(do you really need the "se" here)
Se nos ha roto el coche(the car has broken down on us? why "se" here)
Se le caen las cosas de las manos (things are fallen from his hands')
Los padres no pueden oírse(can I also transform it to "se no pueden oir'")
how about " Los padres se no pueden oir")

Thank you very much for your time.

Answer 1

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Se me caen las llaves(do you really need the "se" here)

Yes. Without "se" you just describe the gravitational effect of falling, how its relative position to the ground diminishes in time. With "se", you are describing a fall as a result of an accident or lost of stable situation. This "se" introduces a small change in meaning or the way things happen.

:

Se nos ha roto el coche(the car has broken down on us? why "se" here)

Here, "se ha roto" means it got broken, i.e. an accident not caused by anyone in particular. Remove "se", and there will be a responsible for the failure (whoever broke the car). "Nos ha roto el coche" means "He broke our car". This "se" turns a transitive verb (a verb where someone does something) into an intransitive one, where things just happen.

:

Se le caen las cosas de las manos (things are fallen from his hands')

Already explained.

:

Los padres no pueden oírse(can I also transform it to "se no pueden oir'")

There are different interpretations here, depending on the context. The first one is a passive reflexive (or medial, depending on the analysis), equivalent to "they cannot be heard". Here, the people who hear the parents are purposefully omitted with this construction, probably because you have no intention to point at whoever hears them.

Another interpretation would be reciprocal: "The parents cannot hear each other".

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how about " Los padres se no pueden oir")

You just shifted the "se" from one place to another. Same sentence.