Learn Hardcore Finnish: Innostunut opiskelija kirjoittaa jokaisen uuden sanan vihkoon huolellisesti. - An enthusiastic student writes every new word in the notebook carefully.

The base verb is innostua – to get excited, to become enthusiastic.
For many type 1 verbs, the past active participle is formed with -nut/-nyt:
- innostua → innostu- + nut → innostunut
- puhua → puhunut
- rakastaa → rakastanut

As an adjective, innostunut means enthusiastic / excited and agrees with the noun in:

number:
- innostunut opiskelija – enthusiastic student
- innostuneet opiskelijat – enthusiastic students
case when declined:
- innostuneen opiskelijan – of the enthusiastic student (genitive)

So in the sentence, innostunut simply functions like an adjective: innostunut opiskelija = an enthusiastic student.

What is the difference between innostunut opiskelija and opiskelija on innostunut?

Both describe a student who is enthusiastic, but the structure and emphasis differ:

innostunut opiskelija
- Adjective directly before a noun.
- Focuses on describing the type of student.
- Similar to English an enthusiastic student.
opiskelija on innostunut
- Predicate structure: subject + olla + adjective.
- More like a state the student is in right now.
- Similar to the student is enthusiastic / excited.

In many contexts they overlap, but:

innostunut opiskelija is more like a permanent or characteristic description, or a neutral label.
opiskelija on innostunut can more strongly suggest a current or newly arisen state (the student has become excited).

Why is the verb kirjoittaa in this form, and how does it agree with opiskelija?

Kirjoittaa is in the 3rd person singular present tense:

Infinitive: kirjoittaa – to write
Present conjugation:
- minä kirjoitan
- sinä kirjoitat
- hän kirjoittaa
- me kirjoitamme
- te kirjoitatte
- he kirjoittavat

The subject opiskelija is 3rd person singular (a/the student), so the correct verb form is also 3rd person singular: kirjoittaa.

There is no separate auxiliary verb like do or does in Finnish; tense and person are all shown in the verb ending.

In jokaisen uuden sanan, why are all three words in the same case and form?

Jokaisen uuden sanan is a noun phrase where all the words agree in case, number, and (where relevant) gender does not exist in Finnish:

jokaisen – genitive singular of jokainen (each, every)
uuden – genitive singular of uusi (new)
sanan – genitive singular of sana (word)

In Finnish, within a noun phrase:

The determiner/pronoun (jokainen),
The adjective (uusi),
The noun (sana)

all take the same case and number:

nominative: jokainen uusi sana
genitive: jokaisen uuden sanan
partitive: jokaista uutta sanaa

Here the phrase is the object of kirjoittaa, and it is a total object in the genitive singular, so everything appears in genitive: jokaisen uuden sanan.

Why is the object jokaisen uuden sanan in the genitive, not in the partitive or nominative?

This is about the Finnish object case system (total vs. partial object):

Genitive object (total object) often appears when:
- The action is seen as complete / bounded.
- The whole of the object is affected.
- The event is not ongoing or incomplete in aspect.

Here:

The idea is that the student writes each word completely into the notebook.
The action conceptually reaches its endpoint for every single word.
Hence jokaisen uuden sanan is in the genitive: it is a total object.

Compare:

Kirjoitan kirjeen. – I write / will write the (whole) letter. (genitive, total)
Kirjoitan kirjettä. – I am writing (some of) the letter. (partitive, ongoing/partial)

So kirjoittaa jokaisen uuden sanan presents the action as fully completed for every word encountered.

Could you also say jokaista uutta sanaa instead of jokaisen uuden sanan? Is there a difference?

Yes, jokaista uutta sanaa is grammatically possible, but there is a nuance:

jokaisen uuden sanan – genitive (total object)
- Emphasises that each new word is written in its entirety.
- More neutral here and very typical.
jokaista uutta sanaa – partitive (partial object)
- Suggests a more ongoing, possibly incomplete process.
- Could be used if you focus on the activity itself:
  - The enthusiastic student is (busy) writing every new word in the notebook – focusing on the process rather than completion.

In many everyday contexts, jokaisen uuden sanan is the more straightforward and usual choice in a simple, factual statement like this one.

What case is vihkoon, and how is it formed from vihko?

Vihkoon is in the illative case, which usually means into / to (inside) somewhere.

Base noun: vihko – a notebook, exercise book
Illative singular: vihkoon – into (a/the) notebook

Formation pattern:

Illative ending is often -Vn, where V repeats the preceding vowel.
vihko → stem vihko-
Add illative: vihko + on → vihkoon
- The o is doubled: o + on → oon

Meaning of key local cases for vihko:

vihko – notebook (basic form)
vihossa – in the notebook (inside, static)
vihkoon – into the notebook (movement into)

In the sentence, kirjoittaa vihkoon is literally writes into the notebook, which corresponds in English to writes in the notebook.

Could we say vihkoonsa instead of vihkoon? What would change?

Yes, vihkoonsa is also possible, and it adds possession explicitly.

vihkoon – into a/the notebook (no explicit owner)
vihkoonsa – into his/her own notebook

Vihkoonsa is formed by:

vihko (notebook) + illative -on
- possessive suffix -sa/‑nsä → vihkoonsa

In many contexts, the owner is clear from context and vihkoon is enough. If you want to stress that it is specifically the student’s own notebook, you can say:

Innostunut opiskelija kirjoittaa jokaisen uuden sanan vihkoonsa huolellisesti.
→ The enthusiastic student writes every new word carefully into his/her own notebook.

What is huolellisesti grammatically, and what is it formed from?

Huolellisesti is an adverb of manner, meaning carefully.

It is derived from the adjective huolellinen (careful):

huolellinen → huolellisesti

The -sti suffix is very common for forming adverbs from adjectives, similar to English -ly:

nopea (fast) → nopeasti (quickly)
selvä (clear) → selvästi (clearly)
varma (sure) → varmasti (surely, certainly)

Placed at the end of the sentence, huolellisesti describes how the action is done: the student writes carefully.

Is the word order fixed? Can we move words like huolellisesti or vihkoon around?

Finnish word order is relatively flexible compared to English. The basic neutral order here is:

[Innostunut opiskelija] [kirjoittaa] [jokaisen uuden sanan] [vihkoon] [huolellisesti].

You can move elements to change emphasis or information structure, while the basic meaning stays similar. For example:

Innostunut opiskelija kirjoittaa vihkoon jokaisen uuden sanan huolellisesti.
Innostunut opiskelija kirjoittaa huolellisesti jokaisen uuden sanan vihkoon.
Jokaisen uuden sanan innostunut opiskelija kirjoittaa vihkoon huolellisesti.
(emphasis on every new word)

Compared to English, you have more freedom, but:

The finite verb usually stays in the second position in neutral sentences.
Moving phrases to the front often signals focus or contrast.

There is no word for a or the here. How is definiteness expressed in this sentence?

Finnish has no articles like a/an or the.

Definiteness and specificity are expressed by:

Context: what has been mentioned or is known.
Pronouns / determiners: e.g. tämä (this), se (that/it), jokainen (each), kaikki (all).
Word order and stress.

In this sentence:

innostunut opiskelija can mean an enthusiastic student or the enthusiastic student, depending on context.
jokainen itself already conveys a universal idea: every new word.
There is no need for a word like the or a, Finnish simply omits it.

So definiteness is inferred from the situation, not grammatically marked with articles.

How would the sentence look in the plural: Enthusiastic students write every new word in their notebooks carefully?

A natural plural version is:

Innostuneet opiskelijat kirjoittavat jokaisen uuden sanan vihkoihinsa huolellisesti.

Changes compared to the singular:

innostunut opiskelija → innostuneet opiskelijat
- adjective and noun both plural nominative.
kirjoittaa → kirjoittavat
- verb becomes 3rd person plural.
vihkoon → vihkoihinsa
- plural illative of vihko with possessive suffix:
  - vihko → vihkoihin (into notebooks)
  - vihkoihin
    - -sa/‑nsä → vihkoihinsa (into their notebooks)

Jokaisen uuden sanan stays singular genitive, because jokainen (each, every) normally takes a singular noun in Finnish, even when the subject and real-world reference are plural.