Learn Hardcore Finnish: Tämä on kirja, joka auttaa minua oppimaan suomea. - This is a book that helps me learn Finnish.

In Finnish, you normally must put a comma between the main clause and a relative clause starting with joka:
- Tämä on kirja, joka auttaa minua oppimaan suomea.

In English, a similar sentence can appear with or without a comma, depending on whether the clause is restrictive or non‑restrictive. Finnish doesn’t use the comma to show that difference; it’s simply a standard rule:

Main clause , joka‑clause
Mies, joka asuu naapurissa, on lääkäri.
= The man who lives next door is a doctor.

Why is it minua and not minä after auttaa?

Minua is the partitive form of minä (I), and auttaa normally takes its object in the partitive case:

Autan sinua. = I help you.
Hän auttaa minua. = He/She helps me.

So in joka auttaa minua oppimaan suomea, the book is helping me, and me must be in the partitive: minua.

You cannot say joka auttaa minä – that form is only used as the subject in the basic form (Minä autan sinua = I help you).

What is oppimaan, and why does it end in -maan?

Oppimaan is the illative form of the 3rd infinitive of oppia (to learn).

Verb: oppia = to learn
3rd infinitive base: oppima-
Illative ending: -an / -en / -hVn ⇒ oppimaan

The structure auttaa + (partitive person) + 3rd infinitive illative means “help someone to do something”:

auttaa minua oppimaan = helps me (to) learn
auttaa sinua muistamaan = helps you remember

So oppimaan here expresses the goal / purpose: into learning.

Why is it suomea and not suomi?

Suomea is the partitive case of suomi (Finnish).

Verbs like oppia, opiskella, puhua, ymmärtää often take languages in the partitive, because the language is seen as an indefinite mass or something you learn/use partially or continually:

Oppia suomea = to learn Finnish
Puhun suomea. = I speak Finnish.
Opiskelen suomea. = I study Finnish.

Using suomi in the nominative here (oppimaan suomi) would be ungrammatical. You need suomea after oppimaan in this meaning.

Can you break down the sentence word by word?

Yes:

Tämä = this (demonstrative pronoun, nominative singular)
on = is (3rd person singular present of olla = to be)
kirja = book (nominative singular; predicate noun)
joka = that / which (relative pronoun, nominative; refers to kirja)
auttaa = helps (3rd person singular present of auttaa)
minua = me (partitive singular of minä)
oppimaan = to learn / into learning (3rd infinitive illative of oppia)
suomea = Finnish (the language) in the partitive singular

Whole: Tämä on kirja, joka auttaa minua oppimaan suomea.
= This is a book that helps me (to) learn Finnish.

Could I say “Tämä kirja auttaa minua oppimaan suomea” instead? What’s the difference?

Yes, that’s perfectly correct, and very natural:

Tämä on kirja, joka auttaa minua oppimaan suomea.
= This is a book that helps me learn Finnish.
Tämä kirja auttaa minua oppimaan suomea.
= This book helps me learn Finnish.

Difference in focus:

Tämä on kirja, joka…
First identifies what kind of thing it is (a book), then describes the book.
Tämä kirja auttaa…
Takes the book as the subject directly and tells you what it does.

In many everyday contexts, Tämä kirja auttaa minua oppimaan suomea is actually more natural and shorter.

Why is the verb olla (on) used here? Why not something like tämä kirja on, joka…?

In Finnish, as in English, you often use olla (to be) to identify or classify something:

Tämä on kirja. = This is a book.
Tämä on kirja, joka auttaa… = This is a book that helps…

The structure “Tämä kirja on, joka …” is not grammatical. The relative pronoun joka needs a noun to refer to (kirja), and it starts its own clause:

Main clause: Tämä on kirja
Relative clause: joka auttaa minua oppimaan suomea

Why is joka in the form joka and not jokaN / jokaA or something else? Does its form change?

Joka behaves like a pronoun and declines for case depending on its role in the relative clause.

Here it is the subject of the relative clause:

joka auttaa minua = which/that helps me → nominative joka

Other cases exist:

jota (partitive): Kirja, jota luen… = The book that I am reading…
johon (illative): Kaupunki, johon muutimme… = The city to which we moved…
jossa (inessive): Talo, jossa asun… = The house in which I live…

So the form joka is chosen because, in this sentence, the book (joka) is doing the action (helping).

Is there any difference between joka and joka auttaa minua oppimaan suomea being with or without commas, like in English restrictive vs non‑restrictive clauses?

In English:

This is a book that helps me learn Finnish. (no comma → restrictive)
This is a book, which helps me learn Finnish. (comma → often non‑restrictive)

In standard written Finnish, the comma is not used to mark restrictive vs non‑restrictive meaning. Instead, the rule is:

Put a comma before a clause starting with joka (or että, koska, kun, etc.), regardless of whether the clause is “essential” or not.

So:

Tämä on kirja, joka auttaa minua oppimaan suomea.

is just the normal way to write it; you don’t get a different nuance by removing the comma – removing it would simply be a punctuation error in formal Finnish.

Could I say “Tämä on kirja, joka auttaa minua opiskelemaan suomea” instead of oppimaan? What’s the difference?

Yes, you can, and it’s grammatically correct:

oppimaan (from oppia) = to learn
opiskelemaan (from opiskella) = to study

Nuance:

oppimaan suomea = helps me to learn Finnish, to acquire the language
opiskelemaan suomea = helps me to study Finnish, focus on the activity of studying (doing exercises, reading grammar, etc.)

In many contexts, oppimaan suomea is more general (to learn), while opiskelemaan suomea highlights the study process.

Why isn’t there any word for the English article “a” before kirja?

Finnish has no articles (no a/an, no the). The noun kirja is just “book”, and you get the idea of “a book” or “the book” from context:

Tämä on kirja.
→ This is a book. / This is the book. (depending on context)

Here, with Tämä on kirja, joka auttaa minua oppimaan suomea, English naturally chooses “a book”, but Finnish doesn’t mark that difference with a separate word. The demonstrative tämä (this) already makes it specific enough in context.