There are always ways to express one idea in another language. It might be clumsy, it might omit some details, but it can work. Of course, if you wanted to express a certain idea about relativity in a tribal language you would have to translate many ideas first on which it depends, but it is not impossible. For some odd reason, certain monolingual Americans seem to disbelieve that and complain about the lack of distinction between simple and progressive tenses in Rejistanian (I didn’t even want them to learn the language, they did so uninvitedly on a wiki-discussion page about it).
So while Rejistanian does indeed lack progressive tenses, it still can indicate the difference betwwen a progressing and a habitual action. One of the ways is by indicating a habitual action as such via ‘sikeva. This carries an anthromorphic component though as it has the connotation of the subject as a conscious actor. Umis’het mi’sikeva ‘okox (The stone falls / Stone-HET 3S-to_do_habitually (INF)fall) would indicate that the stone consciously decides to do so. This might not be what you want to express*. You can use always there instead. But the distinction between sjiki (always in the future) and sjila (always in the past) might be better for another posting. FYI: Umis’het mi’okox sjiki would probably be the cromulent way to express the idea behind “The stone falls”.
Related forms:
sikeva: as habit, habitual(ly), related to a habit
sikeva’tan: habit
*though I occasionally consider the things around me not only to be alive, but very consciously intending to annoy me. 🙂
Rejistanian Word of the Day 
The very idea of someone complaining about the lack of a particular tense distinction in a conlang strikes me as comical. The most appropriate response to me seems like, “Oh, yeah? Well, why not go create your own language!”
It was one of the first reactions to Rejistanian so it probably affected me more than it should have.