SuStel;
Relative clauses and purpose clauses work in entirely different ways for entirely different purposes. It's not just a case of saying "Eh, one type 9 suffix is just like every other!" In English, there is a formal, but not always observed, rule that when you conjoin words or phrases, they should be of like kind, such that one could syntactically substitute for the other without change. It's correct to say if I see you and if I recognize you (two conditional clauses), but it's not correct to say if I see you and while I am eating (a conditional clause and a while-clause). It's correct to say apples and pears (two nouns) but not correct to say apples and happy (a noun and an adjective). And so on.
Ok, now I understand, thanks. I thought it was just a matter of substitution one type-9 with another. In fact, thinking of this matter, I realized that in Greek too we join words/phrases of the same kind. I just hadn't noticed that until now. -- Dana'an https://sacredtextsinklingon.wordpress.com/ Ζεὺς ἦν, Ζεὺς ἐστίν, Ζεὺς ἔσσεται· ὦ μεγάλε Ζεῦ