Aamu on vielä viileä, joten juon teetä sisällä.

The morning is still cool, so I drink tea inside.

Breakdown of Aamu on vielä viileä, joten juon teetä sisällä.

• minä: I
• olla: to be
• juoda: to drink
• joten: so
• sisällä: inside
• viileä: cool
• vielä: still
• tee: tea
• aamu: morning

Questions & Answers about Aamu on vielä viileä, joten juon teetä sisällä.

Why does aamu stay in the basic form, not aamulla?

Both are possible, but they mean slightly different things.

• Aamu on vielä viileä treats aamu (morning) as the topic/“thing” being described: The morning is still cool.
• Aamulla on vielä viileää uses the adessive -lla to mean in the morning, and it often goes with an “existential/weather-like” structure (more like It’s still cool in the morning).
  In your sentence, the speaker is describing the morning as such, so aamu on… is natural.

Why is there on here? Is it always needed?

Yes, in Finnish you typically need the verb olla (on = is) when you link a subject to an adjective or noun (a “copula” sentence):

• Aamu on viileä = The morning is cool. You can omit on only in some special styles (headlines, poetic language), but in normal speech/writing you keep it.

Why is the adjective viileä in this form and not some case ending?

Because it’s a predicate adjective describing the subject aamu, it’s in the nominative (basic form):

• Aamu on viileä. Predicate adjectives usually agree in number (singular/plural) with the subject:
• Aamut ovat viileitä (plural; note the plural form changes)

What does vielä do here?

Vielä most often means still (or sometimes yet) and signals that the situation continues:

• Aamu on vielä viileä = The morning is still cool (not warmed up yet). You’ll also see it in other common patterns:
• Vieläkö…? = Still…?/Yet…? (question)
• En vielä = Not yet.

Why is there a comma before joten?

Because joten introduces a result clause (roughly so/therefore), and in Finnish it’s normal to separate the two clauses with a comma:

• Aamu on vielä viileä, joten… This is standard punctuation for two full clauses joined this way.

How is joten different from koska or siksi?

• joten = so/therefore, emphasizes the result: X, so Y.
• koska = because, emphasizes the reason: Y because X.
  Example: Juon teetä sisällä, koska aamu on vielä viileä.
• siksi = therefore/that’s why, often pairs with koska or stands alone:
  Aamu on vielä viileä. Siksi juon teetä sisällä.

Why is it juon and not the infinitive juoda?

Juon is the 1st person singular present tense form of juoda (to drink):

• juoda = to drink
• minä juon = I drink / I’m drinking Finnish uses the personal verb ending, so the verb changes with the subject.

Why isn’t minä (I) included?

Finnish often drops subject pronouns because the verb ending already shows who does it:

• (Minä) juon = I drink. Including minä is possible, but it adds emphasis/contrast (like I as opposed to someone else).

Why is tea in the form teetä?

Teetä is the partitive singular of tee. Finnish commonly uses the partitive for:

• an uncountable substance (tea as a drink in general)
• an unspecified amount
  So juon teetä is like I’m drinking (some) tea.

Could it be juon teen instead of juon teetä?

Yes, but it changes the nuance.

• juon teetä (partitive) = I’m drinking tea / some tea (process/unspecified amount)
• juon teen (accusative/genitive-looking form) = I’ll drink the tea / I’ll finish the tea (more “whole/complete” or definite)
  In everyday speech about having tea, juon teetä is usually the default.

What exactly does sisällä mean here, and how is it different from sisään?

• sisällä = inside (at/in indoors), location/state (being inside)
• sisään = (to) inside, movement into (going in)
  So:
• juon teetä sisällä = I drink tea inside (already indoors)
• menen sisään = I go inside (movement)

Does sisällä imply “inside the house,” or could it be any inside?

It’s general: inside some contextually understood place (house, café, cabin, etc.). If you want to specify:

• talossa = in the house
• kotona = at home
• kahvilassa = in a café
  But sisällä is natural when the key contrast is simply indoors vs outdoors.