The whole question of when purpose clauses need or don't need subjects should be addressed where purpose clauses are explained. 

-------- Original message --------
From: "luis.chaparro--- via tlhIngan-Hol" <tlhingan-hol@lists.kli.org>
Date: 5/13/23 11:50 AM (GMT-05:00)
To: tlhingan-hol@kli.org
Cc: luis.chaparro@web.de
Subject: Re: [tlhIngan Hol] wishlist for TKD 3ed

> Your suggestions are good, but I think they are 
>> 3. When isn't *-lu'* necessary in purpose clauses when expressing an indefinite subject?

> I'm not sure I understand the question. Can you give examples?

As far as I know, when a purpose clause modifies a *noun*, there is *usually* no subject and no *-lu'*, but there are (unexplained) exceptions to it. See for example the second point here: http://lists.kli.org/pipermail/tlhingan-hol-kli.org/2021-July/058919.html).