Älä käske minua lähtemään.

Because älä is the negative imperative form used when telling one person not to do something.

• ei = the ordinary negative verb used in statements
  
  • En tiedä = I don’t know
• älä = don’t ... ! when speaking to one person
  
  • Älä mene = Don’t go

So Älä käske minua lähtemään means Don’t order/tell me to leave.

For comparison:

• älä = don’t (singular)
• älkää = don’t (plural / polite)

Käske is the imperative singular of the verb käskeä.

Basic verb:

• käskeä = to order, command, tell someone to do something

Imperative forms:

• käske! = order! / tell!
• älä käske! = don’t order! / don’t tell!

So in this sentence:

• älä = negative imperative helper
• käske = the main verb in imperative form

Together: älä käske = don’t tell/order

In Finnish, the subject is usually left out in imperatives because it is already understood.

So:

• Älä käske minua lähtemään = Don’t tell me to leave
• Sinä älä käske minua lähtemään would sound marked or emphatic, something like You don’t tell me to leave

Finnish normally does not include the pronoun unless you want emphasis, contrast, or irritation.

Here minua is the partitive form of minä.

Forms:

• minä = I
• minut = me (total object in some contexts)
• minua = me (partitive object)
• minulle = to me

The verb käskeä commonly takes the person being ordered in the partitive:

• käskeä jotakuta tekemään jotakin
  = to order someone to do something

So:

• minua = me
• Älä käske minua... = Don’t order me...

You use minulle when the meaning is more like say to me in a different structure:

• Älä sano minulle niin = Don’t say that to me

But with käskeä, the normal pattern is partitive person + infinitive construction.

Lähtemään is the illative of the third infinitive of lähteä.

Breakdown:

• verb: lähteä = to leave
• third infinitive stem: lähtemä-
• illative ending: -än
• result: lähtemään

This form is very common after verbs that involve:

• ordering
• telling
• urging
• forcing
• sending
• getting someone to do something

So in this sentence:

• käskeä joku lähtemään = to order someone to leave

A very literal way to think of it is something like:

• order someone into leaving

But the natural English translation is simply:

• tell/order someone to leave

Because after käskeä, Finnish normally uses this pattern:

• käskeä + person (partitive) + verb in -mAAn form

So:

• käskeä minua lähtemään
• käskeä häntä odottamaan
• käskeä lapsia istumaan

Using the plain infinitive lähteä after käskeä would not be the normal structure here.

This is one of those verb patterns that simply has to be learned:

• haluan lähteä = I want to leave
• voin lähteä = I can leave
• älä käske minua lähtemään = don’t tell me to leave

Different verbs require different infinitive constructions.

It can mean any of those, depending on context, but it is usually stronger than ordinary say.

Typical sense of käskeä:

• to order
• to command
• to tell someone to do something in a firm or authoritative way

So Älä käske minua lähtemään could sound like:

• Don’t order me to leave
• Don’t tell me to leave
• Don’t command me to leave

If you wanted a softer idea like ask me to leave, you would use a different verb, such as pyytää.

It is more like Don’t tell/order me to leave.

That is because käskeä is about giving an order or instruction. It does not directly mean forcing in the sense of making something happen physically or causally.

Compare:

• Älä käske minua lähtemään
  = Don’t tell/order me to leave

• Älä pakota minua lähtemään
  = Don’t force me to leave

So käskeä is about authority or commands, while pakottaa is about force.

The pattern is:

• Älä + imperative main verb + person in partitive + third infinitive illative

Applied here:

• Älä = don’t
• käske = tell/order
• minua = me
• lähtemään = to leave

So the structure is:

• Älä käske minua lähtemään
• literally: Don’t order me into leaving
• naturally: Don’t tell me to leave

You can reuse this pattern with other verbs:

• Älä käske minua odottamaan = Don’t tell me to wait
• Älä käske häntä tulemaan = Don’t tell him/her to come
• Älä käske lapsia istumaan = Don’t tell the children to sit down

Yes, Finnish word order is fairly flexible, but the neutral order here is the most natural:

• Älä käske minua lähtemään

This puts things in a clear, standard order:

1. negative imperative
2. main verb
3. object/person affected
4. action they are told to do

You may see other orders for emphasis, for example:

• Minua älä käske lähtemään
  = Don’t you tell me to leave / Me, don’t tell to leave

That version sounds more emphatic or contrastive. For learners, the basic order is the best one to use.

Then you use älkää instead of älä, and the verb gets the plural imperative form.

So:

• Älä käske minua lähtemään = Don’t tell me to leave (to one person)
• Älkää käskekö minua lähtemään = Don’t tell me to leave (to several people / polite)

This is a very useful pair:

• singular: älä + imperative singular
• plural/polite: älkää + imperative plural

It helps to see the steps.

From the verb:

• lähteä = to leave

The third infinitive uses the -mA- element:

• lähte- becomes lähtemä-

Then the illative ending is added:

• lähtemään

So the full form means something like into leaving / to leave depending on context.

You do not need to generate it from scratch every time at first; it is often easiest to learn common chunks:

• mennä → menemään
• tulla → tulemaan
• istua → istumaan
• lähteä → lähtemään

Yes, it is completely natural in standard Finnish.

It sounds fairly direct, though, because both the English and Finnish meanings are direct:

• Don’t tell me to leave
• Don’t order me to leave

In casual speech, people might choose different wording depending on tone, but grammatically and stylistically this sentence is normal standard Finnish.

For example, a softer or more conversational alternative might use another verb, but Älä käske minua lähtemään is perfectly correct and natural.