SuStel:

Sometimes it is speculated that you need a subject if the purpose clause attaches to a
sentence instead of a noun

Because grammar terms confuse me, could you write an example of this ?

I already did. The noun phrase ghojmeH taj is a purpose clause, ghojmeH, attached to a head noun, taj. taj is not the subject of ghojmeH; the knife does not learn anything. It's not an in order that he/she learns knife; it's a knife for learning. There is no subject. It's not an indefinite subject because there's no -lu'; there is simply no subject. This is an infinitive, or as close to an infinitive as Klingon gets.

An even more interesting example is ja'chuqmeH rojHom truce (in order) to confer. The purpose clause has a suffixes that says the subject is a plural entity whose constituents do something to each other, but there is no subject in the phrase. There might be people ready to confer during a truce, but the phrase doesn't say that.

Or take the simple vutmeH 'un pot for preparing food. The pot is a pot for preparing food whether or not there is someone about to prepare food in it. vutmeH has no subject, implied or otherwise.

But there are tons of examples where a purpose clause, attached to a sentence instead of a noun, gets prefixes and suffixes and a subject. Heghlu'meH QaQ jajvam is a well-known one. Or cha'puj vIngevmeH chaw' HInobneS, which even has an object.

Given that the distinction seems to be "infinitive" for nouns and "finite" for sentences, I probably should have written jatlhqu'lu'meH. *shrug*

-- 
SuStel
http://trimboli.name