What is the difference between δικός μου and δική μου? Does it just change when the subject is plural?
Δικος μου etc changes according to the person: "I, you, he.../ the number singular or plural and the gender of the object. Note that the gender masculine, feminine or neuter does not refer to the person but to the grammatical use of the word. So, "το κορτισι (the girl) is neuter, η καρέκλα (the chair) is feminine etc. On the top left of the exercise page, you will see Tips & notes. Click on that to get some more information about this.
I find this incredibly confusing: a girl (obviously female, by definition) is neuter, but a chair (inanimate object and therefore devoid of any sex whatsoever) is feminine. I wish I could understand where it all comes from!
Some things have explanations others don't. Languages evolve over time and adopt various means of expression.
However, just try to remember when we say masculine, feminine and neuter we are not referring to men, women etc these are jus t names to describe how the words are used.
Don't worry about what they are called just get used to the sentences.
If you have access to the web course you will find a lot of information in the Tips & notes which are just below the Lessons on your Homepage.
Your question is similar to the one just below and there is a reply to that one given by mizinamo. I think that will help.
I'm sorry: the only post by mizinamo that I can see in this thread says "Roughly, "own"." which is not much of a help and I can't find anything else like my question on this page.
Well, what mizinamo wrote was "that's a different sentence". Meaning: "The cat is not mine." and "It's not my cat." are different. They may result in a similar interpretation and impart similar knowledge but as we are teaching a language with its many different means of expression we need to maintain the correct translation of each sentence.
If we say "There is an apple and an orange on the table." or "There is an orange and an apple on the table." I'm giving you the same information. But the sentences are not the same. And since Duolingo's method of teaching involves examples acquainting you with how the language works and not with analyzing it we need to show you how it is used. Of course wherever possible we give explanations but in some cases there are none so you need to become accustomed to the usage.
And since as mentioned above languages are based mostly on usage it's necessary to become acquainted with the way things are expressed.
You will find many explanations in the Tips¬es.