Learn Hardcore Finnish: Laitan kirjan laukkuun, jotta muistan palauttaa sen huomenna. - I put the book in the bag so that I remember to return it tomorrow.

Laitan is the 1st person singular present tense of laittaa (I put / I’m going to put). In this context it often implies a near-future intention as well as a present action.

Panen also means I put, but it’s less common in everyday neutral speech and can sound old-fashioned or overly formal in many contexts.
Laitoin would be past tense (I put / I placed), which would change the time reference.

Why is kirja in the form kirjan?

Kirjan is the total object form (often called accusative; with nouns it looks like the genitive -n). It’s used because the action is seen as complete: you’re putting the book into the bag as a whole, finished action. Compare:

Laitan kirjan laukkuun. = I put the (whole) book into the bag (completed result).
Laitan kirjaa laukkuun. = I’m putting a book / some of the book into the bag, or focusing on the process (usually odd here unless context makes it ongoing/partial).

What does laukkuun mean grammatically, and why that ending?

Laukkuun is illative case, meaning into (movement into something).

Base word: laukku = bag
Illative: laukkuun = into the bag

This sentence needs the “into” meaning because you’re moving the book from outside to inside the bag.

How do I know when to use -ssa/-ssä vs -Vn (like laukussa vs laukkuun)?

Use:

Inessive -ssa/-ssä for location in (no movement): kirja on laukussa = the book is in the bag.
Illative -Vn (here -uun) for movement into: laitan kirjan laukkuun = I put the book into the bag.

So: laukussa = in the bag (static), laukkuun = into the bag (direction/motion).

What is jotta, and why is it used here?

Jotta means so that / in order that and introduces a purpose clause: you put the book in the bag for the purpose of remembering to return it tomorrow. It’s a common way to express intention/purpose, especially when the subject is the same in both clauses (though it also works when the subject changes).

Why is there a comma before jotta?

In Finnish, a comma is typically used before a subordinate clause introduced by conjunctions like jotta, koska, että, etc. So:

Laitan kirjan laukkuun, jotta ... is standard punctuation.

Why is it muistan palauttaa (two verbs in a row)? What form is palauttaa?

Muistan (I remember) can take another verb in the 1st infinitive form to express “remember to do something.”

muistan
- palauttaa = I remember to return

Palauttaa here is the basic dictionary form (the 1st infinitive). Many Finnish verbs work like this: a finite verb + an infinitive.

Could it also be muistan palauttamisen or something similar?

Yes, but it changes the structure and nuance:

Muistan palauttaa sen. = I remember to return it (remembering an obligation/action).
Muistan palauttamisen. = I remember the returning (more like recalling the event/idea of returning, not necessarily remembering to do it at the right time).

For “remember to do something,” muistaa + infinitive is the most direct.

What does sen refer to, and why not se?

Sen is the object form of se (it). It refers back to kirjan (the book): return it.

se = it (subject form)
sen = it (object/genitive-looking form)

Because palauttaa needs an object (return something), Finnish uses sen here.

Why is palauttaa sen “total object” too? Could it be palauttaa sitä?

Palauttaa sen treats the returning as a complete, bounded action: you return the item fully. Palauttaa sitä would suggest something more ongoing/partial (or could appear in certain contexts like talking about the process, repeated attempts, or an indefinite/unknown referent). With returning a specific book, sen is the natural choice.

Does Finnish need a word for the in this sentence?

Finnish has no articles (the / a). Definiteness is usually understood from context. Here, kirjan can be understood as the book (a known book) or a book depending on context, but the structure strongly suggests a specific one (especially since you later say sen, “it,” referring back to it).

Is the word order flexible? Could I say Jotta muistan palauttaa sen huomenna, laitan kirjan laukkuun?

Yes. Finnish word order is relatively flexible and often used for emphasis or information flow. Both are correct:

Laitan kirjan laukkuun, jotta muistan palauttaa sen huomenna. (neutral, action first)
Jotta muistan palauttaa sen huomenna, laitan kirjan laukkuun. (purpose first, slightly more “in order to…” framing)

The meaning stays essentially the same.

Where can huomenna go, and what does it modify?

Huomenna = tomorrow. It most naturally modifies the returning action: you plan to return it tomorrow. Common placements include:

... palauttaa sen huomenna. (most neutral)
... huomenna palauttaa sen. (more emphasis on “tomorrow”)
Huomenna can also be moved earlier for emphasis, but the default is near the verb it relates to.