I have not found any explanation on Duolingo as to when the partitive is used, so have had to try and figure it out for myself. I gather it is when the amount of something is not quantifiable. So why is that the case with "this juice" as in this example? Why is "this juice" (in this container so a specific amount I would have thought) different from "this potato?" Normally if the partitive is used, both the noun and the adjective seem to me to be partitive but in this case it is only the adjective. I would be so grateful if someone could explain. It is difficult trying to work it out for myself.
Look for the article titled ""Unofficial" grammar tips for all Finnish learners - FAQ list (Updated on August 5th, retitled)" with "Finnish:" as prefix (It is in the Finnish discussion group). It tells you some of what you want to know, that Duolingo did not (yet) put into tips.
Mehu is the subject here. I don't think partitive is in order for the subject, unless prepended by "this glass of" or " this cup of" which would force mehu into partitive, even as a subject. So mehu usually gets partitive as an object.
Am I right, guys?
Bloody hell, I always fall for this one. Thank you for explaining this. For some reason I have real trouble with partitive, even with the article you guys pinned on the general forum. I still get it wrong. Thank you for reminding me!