The prepositions of the Fergiartic show several pairs that are distinguished by an -i.
The rules are:
pure preposition = direction
preposition + -i = location
ad (up - to), adi (at), ambi (at, around, round about), an (up - to, on - to), ani (at, on), anti (apart), apa (of, away from), ati (over, beyond), dis (against), du (to, after), ess (out - of), essi (after, afterwards [temporal.]), ge (behind), hopa (below), hopu (down, down - from), in (in - to), ini (in), inter (between), opi (for), opri (over), per (through), pra (before [temporal]), preti (opposite to, beside, next to), pru (before), son (together with, with), sona (with, though, by [instrumental]), ud (out of), ûner (under).
As prefixes of verbs and nouns are used: ad, amb(i), an, ant(i), ap(a), at(i), dis, du, ess, ge, hop(u), in, inter, opri, per, preti, pru, son, ûner.
akken (although); anite ([so] that not), anken (if not), atte (besides, and), hise (so, then), hite (that, so that), hved (but, though), kai (therefore, because), kote (whereby, in which), on (or), san (if), tan (although, though).
Anm. For further conjunctions see III.5.