"This bottle is green."

Translation: यह बोतल हरी है।

[Aakhil6]

So, is बोतल female noun?

[Zerenei]

Indeed. It would say हरा otherwise

[duolingonaut]

When to use इस and when to use यह - I'm at a loss here. Google is not my friend.

Are इस and उस for emphasis? Not that one, but that one?

[Zerenei]

Okay listen to Aakhil6, he was right, इस, उस, इन, उन are used when a postposition follows. That includes को, से, पर, ने, के, this works when the postposition simply follows the pronoun (उसने, इसको, उनको, इसके साथ​) or when the postposition follows the additional noun, (इस लड़के ने सेब खाया = This boy ate an apple, इस मेज़ पर बहुत सारे बिल्लियाँ हैं = There are many cats on this table, मैं उस किताब के बारे में बोलता हूँ = I talk about that book.

[Zerenei]

यह when it's the subject, इस when it's the object. (Same for वह and उस​.) यह सेब लाल है = this apple is red. मैं इस सेब खाता हूँ = I eat this apple. And ये and वे become इन and उन​.

[Aakhil6]

Wait! One can't say like that मैं इस सेब खता हूँ, the right one is मैं यह सेब खता हूँ. The word यह transforms to इस when there is a postposition like में, पर, के साथ etc. (Same with वह to उस, ये to इन and वे to उन.)
The appropriate example would be इस सेब के साथ नाश्ता करो (Have breakfast with this apple).
Forgive if there are mistakes and I'm a learner.

[Zerenei]

Haha I'm a learner as well, my bad if I made a mistake there. I just go off of where I have heard it before, I figured it is used as the object, but maybe it's instead used with postpositions. Will ask a native speaker for clarification

[duolingonaut]

Thanks (both of you) for taking so much time to answer my question. In the meantime I found the answer elsewhere on this forum and subsequently verified it in the notes (so you have to look under food for this) and
elsewhere. The keyword in the answer to this as well as to so many other questions is: oblique.

I wanted to modify my question, but I couldn't find it again until you answered it. Duolingo doesn't make it easy for me to find my old comments. I suppose I could save a link every time I comment. But I don't.

[Aakhil6]

Thanks to you again!! You provided the link of notes in here. And I learnt a lot from that. That's really wonderful.
Now I can confidently say यह transforms to इस when
1) there are propositions,
2) In dative cases for indirect objects,
3) In sentences which have चाहिए , पसंद होना, etc.
Now it's clear that यह to इस can't be in oblique (objective) cases.

[khmih]

Confused