Learn Hardcore Finnish: Työpaikalla johtaja muistuttaa, että sinun ei pidä vastata viesteihin yöllä. - At work the manager reminds you that you must not reply to messages at night.

työpaikassa (inessive, in the workplace) focuses on being physically inside the workplace as a space.
työpaikalla (adessive, at the workplace) is the normal idiomatic way to say “at work” in general, not emphasising being inside a building.

So Työpaikalla johtaja muistuttaa… is best read as “At work, the boss reminds (you)…”, talking about the situation or context of work, not the room you’re standing in. Using työpaikassa here would sound unusual and too concrete.

What does muistuttaa mean, and how is it different from muistaa?

muistaa = to remember
- Minä muistan. = I remember.
muistuttaa = to remind (someone)
- Johtaja muistuttaa työntekijöitä. = The boss reminds the employees.

In the sentence johtaja muistuttaa, että…, muistuttaa introduces what the boss is reminding people of, and the content comes in the että-clause that follows.

What is the role of että here, and why is there a comma before it?

että is a conjunction usually translated as “that” in English. It introduces a subordinate clause that functions as the content of the reminder:

Johtaja muistuttaa, että… = “The boss reminds (you) that…”

The comma is required because in Finnish you normally put a comma between a main clause and a subordinate että-clause:

(Main) Johtaja muistuttaa,
(Subordinate) että sinun ei pidä vastata viesteihin yöllä.

Why is it sinun ei pidä and not sinä et pidä?

There are two different structures:

sinä et pidä = “you don’t like” (emotion, opinion)
- pitää (jostakin) = to like (something)
- Sinä et pidä kahvista. = You don’t like coffee.
sinun pitää / sinun ei pidä + infinitive = “you must / must not (do something)”
- pitää tehdä in this pattern expresses obligation, not “to like”.
- The subject is in the genitive: minun, sinun, hänen…
  - Minun pitää lähteä. = I must leave.
  - Sinun ei pidä vastata. = You must not answer.

So sinun ei pidä vastata means “you must not answer”, not “you don’t like to answer”. The form sinä et pidä vastata would be ungrammatical in this meaning.

Why is it sinun (genitive) and not sinä (nominative)? What is this pattern?

The obligation construction [GENITIVE pronoun + pitää + infinitive] is a very common Finnish structure:

Minun pitää mennä. = I must go.
Sinun pitää lukea. = You must read.
Meidän ei pidä myöhästyä. = We must not be late.

So the “subject” of the obligation is in genitive: minun, sinun, hänen, meidän, teidän, heidän. The verb pitää stays in 3rd person singular.

In the negative, you add ei:

Sinun ei pidä vastata. = You must not answer.

So sinun is required by this grammar pattern; sinä ei pidä is incorrect.

Why is the verb form pidä here, not pitää or pidät?

In Finnish negation, the personal information (person/number) is carried by ei / et / emme, and the main verb goes into a special connegative form.

Affirmative: sinun pitää vastata (you must answer)
Negative: sinun ei pidä vastata (you must not answer)

So:

pitää is the dictionary form.
pidä here is the connegative form used after ei.
You never write sinun ei pitää or sinun ei pidät. The correct pair is always:
- pitää (affirmative) ↔ ei pidä (negative).

Could you say ei sinun pidä vastata instead of sinun ei pidä vastata?

You might occasionally hear Ei sinun pidä vastata… with ei at the very beginning of the sentence for emphasis, but the basic neutral word order has the subject/actor first and ei immediately before the verb:

Neutral: Sinun ei pidä vastata viesteihin yöllä.
Emphatic spoken variant: Ei sinun pidä vastata viesteihin yöllä.

In the middle of the clause, you don’t move ei away from the verb; sinun ei pidä is the normal structure.

Can sinun be left out? What changes if we omit it?

Yes, you can omit sinun if it is clear from context who is being talked about, or if you want a more general rule:

Johtaja muistuttaa, ettei viesteihin pidä vastata yöllä.
- Literally: “The boss reminds that one must not answer messages at night.”

Here the subject is unspecified (like English “one”, “people”, or generic “you”).
With sinun ei pidä, the rule is directed specifically at you (or the person being addressed).

So:

sinun ei pidä vastata = you (in particular) must not answer.
ei pidä vastata = one must not answer / it should not be answered.

Why is it vastata viesteihin and not something like vastata viestit?

This is about verb–case government (rections). The verb vastata (“to answer/respond”) normally takes its target in the illative case:

vastata johonkin = to answer something / to respond to something
vastata viesteihin = to answer messages / to respond to messages

So:

viesti = a message (nominative)
viesteihin = into/to the messages (plural illative)

Using viestit (nominative plural) would mean something more like “to answer the messages (as subject)” and would not fit the pattern of vastata, which expects its object in the illative case.

What case is viesteihin, and when is that case used?

viesteihin is the illative plural of viesti (“message”).

Illative often corresponds to “into / to / onto”:

talo → taloon = into the house
kaupunki → kaupunkiin = to the city
viesti → viestiin = to the message
viestit → viesteihin = to the messages

Here it is required by the verb vastata (vastata + illative). So viesteihin = “to (the) messages” in the sense of “responding to them”.

Why is yöllä used, and what does the -llä ending mean with time words?

yöllä is the adessive singular of yö (“night”), and with time expressions, -lla/-llä often corresponds to “at (a time)”:

yöllä = at night
päivällä = in the daytime
kesällä = in (the) summer
jouluna (another time form) = at Christmas

So viesteihin yöllä = “(to) messages at night.”
You wouldn’t normally say yössä here; yössä would sound more like “in the night (inside the night)” and is used in different contexts. Yöllä is the standard expression for “at night.”

Could the sentence be said more directly, like a command, instead of using muistuttaa, että…?

Yes. The current sentence is indirect: it reports what the boss reminds you of.

A direct command would use the negative imperative:

Johtaja sanoo: “Älä vastaa viesteihin yöllä.”
- The boss says: “Don’t answer messages at night.”

Your sentence wraps this command inside reported speech:

Työpaikalla johtaja muistuttaa, että sinun ei pidä vastata viesteihin yöllä.
- At work, the boss reminds (you) that you must not answer messages at night.

So älä vastaa = direct “don’t answer”, while sinun ei pidä vastata = more descriptive/indirect “you must not answer.”

Is ei pidä the same as ei saa? Do they both mean “must not”?

They are close but not identical:

sinun ei pidä vastata
= you should not / must not answer
- Focus on recommendation / norm / proper behaviour.
- Often a bit softer or more “this is not appropriate”.
sinun ei saa vastata
= you are not allowed to answer
- Focus on permission.
- More like a rule: it is forbidden.

In many contexts they can both be translated as “must not”, but:

The boss emphasising company policy might say either, depending on whether it’s more “not appropriate” (ei pidä) or strictly “not allowed” (ei saa).