A bent rule?

Remember the little word si? I have a post about it here, where it has strict rules about how it is used. Namely, it always refers to the subject of the verb. But there are some occasions where it bends those rules, and those are in certain fixed expressions.

per si (mem)
by itself/themself (alone), by means of themself/itself (alone):

oni komprenas liajn gestojn per si mem
his gestures by themselves alone are understood

Notice how oni is the subject here, but that si refers to the gestures.

inter si
between/among themselves, mutually with each other

“Lingvo Internacia” kaj “lingvo tutmonda” estas du tute malsamaj objektoj, kiujn miksi inter si oni neniel devas
“International language” and “Worldwide language” are two totally different things, which must in no way be mixed up with each other

Notice how the direct object is kiujn referring to the two different terms, and so si is referring to the direct object! I’m just using these examples to show those times that this rule is broken, but that doesn’t mean that the fixed expressions always work this way:

ili parolis inter si
they spoke/talked among themselves

Si here is properly referring to the subject. Context will usually make this clear!

siatempe
in/at that time, in the concerned time, etc.

It can be used regardless of what the subject is, because it just always refers to an implied time, independent of the subject:

mi volis siatempe proponi regulon
I wanted at the time to propose a rule

If it had to refer to the subject strictly (like“je sia tempo" would have to), then it would be “at my time”. But it doesn’t!

Check out the PMEG page from which I took most of my examples. You’ll also find a couple more expressions there too! Good ole PMEG.