Questions & Answers about Tämä kirja on minun.
How does the word minä (I) become minun (mine) here?
To show possession, Finnish uses the genitive case, which adds an -n to the end of the word. For the pronoun minä, the stem changes slightly to minu-, and adding the -n gives us minun.
Does minun mean "my" or "mine"?
It means both! Finnish doesn't have separate words for "my" and "mine". Depending on the sentence structure, minun works as both. Here, it stands alone after the verb, so it translates perfectly to "mine".
Could I change the word order to "Tämä on minun kirja"?
You can, but it changes the focus slightly to mean "This is my book" instead of "This book is mine". Notice how the Finnish word order matches the English word order in both cases: Tämä kirja on minun (This book is mine) versus Tämä on minun kirja (This is my book).
Is minun what I will actually hear native speakers say in casual conversation?
In written Finnish or formal speech, yes. However, in everyday spoken Finnish, minun is almost always shortened to mun. You will very often hear people say Tämä kirja on mun.