Learn Hardcore Finnish: Minusta tämä selitys on epäselvä. - In my opinion, this explanation is unclear.

Minusta is the elative case (the -sta/-stä case) of minä (I).
Literally it means from me, but in this kind of sentence it idiomatically means in my opinion or I think.

So Minusta tämä selitys on epäselvä is structurally something like From my point of view, this explanation is unclear, which English simply renders as I think this explanation is unclear or In my opinion, this explanation is unclear.

Why is it minusta and not minä or minun at the beginning?

Finnish pronouns change form according to case:

minä = I (nominative, used as a subject)
minun = my (genitive, used as a possessor)
minusta = from me (elative, used here as a “source of opinion”)

In this sentence, the pronoun is not the grammatical subject; tämä selitys is.
Instead, minusta functions as an adverbial that shows whose viewpoint the statement is made from, so it must take the elative ending -sta, not the basic form minä or the genitive minun.

Is Minusta equivalent to “I think” or “In my opinion”? Are there any nuances?

It overlaps strongly with both “I think” and “In my opinion”.

Minusta tämä selitys on epäselvä ≈ I think this explanation is unclear / In my opinion this explanation is unclear.

Nuance-wise:

Minusta sounds quite neutral and natural in everyday speech and writing.
It doesn’t explicitly mention “thinking” or “opinion” (no word like “think”), but in this pattern it’s automatically understood as subjective opinion.

If you want to sound a bit more formal or emphatic about the opinion aspect, you might choose minun mielestäni instead.

How is minusta different from minun mielestäni, minun mielestä, and mielestäni?

All of these can introduce an opinion, but they differ in formality and structure:

Minusta tämä selitys on epäselvä.
Short, very common, neutral. Literally from me.
Minun mielestäni tämä selitys on epäselvä.
More explicit: literally from my mind, this explanation is unclear.
Slightly more formal or emphatic than minusta.
Mielestäni tämä selitys on epäselvä.
Means the same as minun mielestäni; the -ni at the end of mielestäni already means my.
Often used in written or somewhat formal style.
Minun mielestä tämä selitys on epäselvä.
This is colloquial spoken Finnish. In standard written Finnish you are expected to say minun mielestäni.
You will hear mun mielestä very often in speech.

Can I leave out Minusta and just say Tämä selitys on epäselvä? Does it sound different?

Yes, you can say Tämä selitys on epäselvä.

Tämä selitys on epäselvä.
Sounds like a general, more “objective” statement: This explanation is unclear (as a fact).
Minusta tämä selitys on epäselvä.
Makes it explicit that this is your judgement or opinion.

So adding minusta softens it a bit and frames it as personal opinion rather than a universal truth.

Can I move minusta to another position, like Tämä selitys on minusta epäselvä?

Yes, Finnish word order is fairly flexible, and minusta can move:

Minusta tämä selitys on epäselvä.
Neutral; introduces your viewpoint first.
Tämä selitys on minusta epäselvä.
Also correct; now the focus is slightly more on the explanation, and minusta feels like an added comment: This explanation is, to me, unclear.
Tämä selitys on epäselvä minusta.
Possible, but a bit more marked; it can sound like you are contrasting your opinion with someone else’s.

All of these are grammatically fine; the differences are subtle nuances of emphasis.

Why is it tämä selitys, not tämän selitys?

Tämä selitys is the subject of the sentence, so both words stay in the nominative:

tämä = this (nominative)
selitys = explanation (nominative)

Together: tämä selitys = this explanation (as the subject).

Tämän selitys uses tämän, which is the genitive form of tämä. That would normally mean the explanation of this (thing) and would need some context or something it belongs to. For example:

Tämän asian selitys on pitkä.
= The explanation of this matter is long.

In your sentence, you just want this explanation as the subject, so you use tämä selitys (nominative), not tämän selitys.

Why is epäselvä in its basic form? When would it change?

Epäselvä is an adjective used as a predicative: it describes the subject tämä selitys.
In such sentences, the predicative adjective usually agrees with the subject in number (and sometimes case). Here:

Subject: tämä selitys (singular)
Predicate adjective: epäselvä (singular, nominative)

If the subject were plural, the adjective would change:

Nämä selitykset ovat epäselviä. = These explanations are unclear.

Here selitykset is plural, and epäselviä is plural too. (You may encounter epäselvät as well; there is some nuance between nominative and partitive plural, but that’s a more advanced topic.)

In your original singular sentence, epäselvä is in the basic form because it matches the singular subject.

What is the relationship between selvä and epäselvä, and what does the prefix epä- do?

Selvä means clear, obvious, evident.

The prefix epä- is a common way in Finnish to form a kind of opposite or negative version of an adjective or noun. So:

selvä → epäselvä (clear → unclear)
varma → epävarma (sure → unsure)
onnistuminen → epäonnistuminen (success → failure)

So epäselvä is simply not clear / unclear / confusing.

Why do we need the verb on here? Could I say Minusta tämä selitys epäselvä without it?

You need the verb olla (to be) in sentences like this:

Tämä selitys on epäselvä.
Minusta tämä selitys on epäselvä.

Leaving out on (Minusta tämä selitys epäselvä) is ungrammatical in standard Finnish.
Finnish does allow dropping on in some very limited colloquial patterns (like Se hyvä in very casual speech), but in normal, correct language here, on is required.

Does minusta always express opinion, or can it mean something else?

Minusta is simply the elative form of minä, so its basic meaning is from me.
Expressing opinion is just one very common use, especially at the start of sentences like yours.

Other uses include, for example:

Tämä tuntuu minusta vaikealta. = This feels difficult to me.
Lähtö minusta ei ole helppoa. = Leaving me is not easy.
Literal spatial uses (less common with minusta, but possible in principle): He took it from me would normally be Hän otti sen minulta, using -lta, but the idea is similar (case marking on the pronoun).

So in your sentence it means in my opinion, but the form itself is a general case form, not limited to opinions.

How would I say the same thing for other persons, like “you think”, “he/she thinks”, “we think”?

You follow the same -sta/-stä pattern with the appropriate pronoun:

Sinusta tämä selitys on epäselvä.
= You think this explanation is unclear. / In your opinion, this explanation is unclear.
Hänestä tämä selitys on epäselvä.
= He/She thinks this explanation is unclear.
Meistä tämä selitys on epäselvä.
= We think this explanation is unclear.
Teistä tämä selitys on epäselvä.
= You (plural) think this explanation is unclear.
Heistä tämä selitys on epäselvä.
= They think this explanation is unclear.

The structure stays the same; only the pronoun (and its -sta/-stä ending) changes.