Learn Hardcore Finnish: Laturi jäi kotiin, joten tilaan uuden netistä. - The charger was left at home, so I will order a new one from the internet.

Finnish often uses jäädä to say that something “ended up staying/was left behind,” without naming who caused it. Laturi jäi kotiin is neutral and common, especially for accidental situations. If you want to explicitly say you left it, use:

Jätin laturin kotiin. = I left the charger at home.
Unohdin laturin kotiin. = I forgot the charger at home.
More impersonal: Laturi unohtui kotiin. = The charger (accidentally) got forgotten at home.

Why is it kotiin and not kotona after jäi?

With jäädä, Finnish typically uses the illative (directional “into/to”) to express the resulting place: jäädä kotiin = remain/stay home. Compare:

kotiin (illative) = to (the) home, into home
kotona (inessive) = at home (state/location)
kotoa (elative) = from home (source) So Laturi jäi kotiin means “the charger ended up at home.” Saying Laturi jäi kotona is ungrammatical.

Why is kotiin spelled with two i’s?

The illative ending for words like koti is “-in,” and a final i in the stem doubles before that ending. Hence koti + -in → kotiin. Another example: baari → baariin.

What does joten do here, and is the comma before it necessary?

Joten is a coordinating conjunction meaning “so/therefore,” linking two main clauses. Standard Finnish uses a comma before it: ..., joten .... You could also start a new sentence with an adverb like Siksi or Niinpä:

Laturi jäi kotiin. Siksi tilaan uuden netistä.
Laturi jäi kotiin, joten tilaan uuden netistä.

Could I start the sentence with Joten?

Informally, yes: Joten tilaan uuden netistä. In careful writing, many prefer Siksi/Niinpä at the start of a sentence, or keep joten after a comma joining two clauses.

Why is tilaan (present tense) used for a future action?

Finnish has no dedicated future tense. The present indicative often covers the immediate or planned future. Tilaan naturally means “I’ll order” here. If you want to emphasize intention, you can say Aion tilata uuden = “I intend to order a new one.”

What exactly is uuden? Why not just uusi?

Uuden is the genitive singular of uusi (“new”) and acts as a “new one.” In Finnish, a singular total object in an affirmative clause takes the “total object” case, which for adjectives is the genitive. Since the understood noun (laturi) is the object, the adjective alone must appear in the same object case: tilaan uuden (laturin).

Could it be uutta instead of uuden?

Uutta (partitive) would suggest an incomplete/process-like action (e.g., “I’m in the process of ordering a new one”), which doesn’t match the simple, completed intention conveyed by tilaan here. So uuden is the default choice.

Why is there no word like “one” after uuden?

Finnish typically omits the noun and lets the adjective stand alone. Uuden here means “a new one,” with the noun (laturi) understood from context. If you want to say it explicitly: tilaan uuden laturin.

What case is netistä and why that case?

Netistä is the elative case (-sta/-stä), meaning “from the internet,” i.e., ordering from an online source. Common patterns:

netissä = on the internet (location)
nettiin = to the internet (into, direction)
netistä = from the internet (source) With verbs like “order/buy,” Finnish uses the source case: tilata/ostaa netistä.

Could I say verkosta instead of netistä?

Yes. Verkosta (from “the web/network”) is slightly more neutral/formal; netistä is very common and colloquial-neutral. Both mean “online, from the internet.”

Is the word order tilaan uuden netistä fixed? Can I say Tilaan netistä uuden?

Both are possible. The neutral default is object before the source phrase: Tilaan uuden netistä. Moving netistä earlier (Tilaan netistä uuden) can emphasize “from the internet” (as opposed to a physical store).

Why not mark possession, like “my charger”?

Finnish often omits possessive marking when it’s clear from context. Laturi jäi kotiin naturally implies it’s your charger. If you want to be explicit:

Neutral: Mun laturi jäi kotiin. (colloquial)
Formal: Laturini jäi kotiin.

How is the tone different between Laturi jäi kotiin and Jätin laturin kotiin?

Laturi jäi kotiin: Neutral/accidental result; agent not mentioned; sounds less blameful.
Jätin laturin kotiin: Explicitly “I left it”; more agentive/responsibility.
Laturi unohtui kotiin: “It got forgotten”; emphasizes accident.

Could I use pysyä instead of jäädä here?

Not naturally. Pysyä = “to remain/keep (being)” and doesn’t work for “got left behind.” For staying on purpose, a person can say Jään kotiin (“I’m staying home”), but for an item unintentionally left, jäädä is the idiomatic choice: Laturi jäi kotiin.

Is there anything irregular about uusi → uuden?

Yes. Uusi has a stem uude- in many case forms: uuden (genitive), uuteen (illative), uudessa (inessive), etc. So uuden is the expected genitive form used here as the total object (“a new one”).