Kokeile tätä takkia.

A natural translation is Try this jacket or Try on this jacket.

A small nuance:

• takki can mean jacket or coat, depending on context.
• kokeilla means to try, to test, or to give something a try.

So in a clothing-shop situation, this sentence would usually mean Try this jacket on.

kokeile is the imperative singular form of the verb kokeilla (to try).

So:

• kokeilla = to try
• kokeile! = try!

It is the form you use when telling one person to do something:

• Kokeile tätä takkia. = Try this jacket.

Finnish usually does not need a separate subject pronoun when the verb form already shows who is being addressed.

Here, kokeile already means you try! (singular), so sinä is unnecessary.

You could say:

• Sinä kokeile tätä takkia.

But that sounds marked or contrastive, as if stressing you in particular. Normally, Finnish just says:

• Kokeile tätä takkia.

Because both words are in the partitive singular, not the basic dictionary form.

The basic forms are:

• tämä = this
• takki = jacket / coat

In the sentence, they become:

• tätä
• takkia

This happens because the verb kokeilla usually takes its object in the partitive.

So:

• kokeilla takkia = to try a jacket
• kokeilla tätä takkia = to try this jacket

It is the partitive singular.

Both words agree with each other:

• tätä = partitive singular of tämä
• takkia = partitive singular of takki

Finnish modifiers usually match the noun in case and number, so if the noun is partitive singular, the demonstrative is too.

Many Finnish verbs regularly take the partitive object, and kokeilla is one of them.

The idea is that trying something is not viewed as a completed action affecting the whole object in the same way as, for example, buying or taking it. It is more like testing or having a go.

So Finnish says:

• kokeilla autoa = try a car
• kokeilla reseptiä = try a recipe
• kokeilla takkia = try a jacket

For this reason, Kokeile tämä takki would not be the normal form here.

tätä is the partitive singular form of tämä.

This is an irregular-looking but very common pattern:

• tämä = this
• tämän = this (genitive)
• tätä = this (partitive)

So in tätä takkia, tätä means this in the same case as the noun.

takkia is the partitive singular of takki.

The basic form is:

• takki

The partitive singular is:

• takkia

This is a common noun pattern in Finnish. For this word, the partitive keeps the strong kk:

• takki
• takkia

Compare that with another form:

• takin = of the jacket

So different cases can change the stem in different ways.

It can mean either jacket or coat, depending on context.

In everyday Finnish, takki is a broad word for an outer garment. English often distinguishes more carefully between jacket and coat, but Finnish may simply use takki.

So without more context, Kokeile tätä takkia could mean:

• Try this jacket
• Try this coat

It is understandable and natural, but there is also a more specific verb: sovittaa.

• kokeilla = try, test
• sovittaa = try on (especially clothes)

So in a shop, you may hear both:

• Kokeile tätä takkia.
• Sovita tätä takkia.

The second one is more specifically about putting the garment on to see how it fits.

It is a normal singular imperative, so it can sound:

• friendly,
• encouraging,
• direct, depending on tone and situation.

It is fine in many everyday contexts, for example if a shop assistant is speaking casually.

If you want to be more polite or softer, Finnish often uses other forms, such as:

• Voisitko kokeilla tätä takkia? = Could you try this jacket?
• Kokeilkaa tätä takkia. = Try this jacket. / Please try this jacket. (plural or polite)
• Kannattaisi kokeilla tätä takkia. = It would be worth trying this jacket.

Yes, but Kokeile tätä takkia is the most neutral order.

Finnish word order is fairly flexible, but changing it usually changes emphasis.

For example:

• Kokeile tätä takkia. = neutral
• Tätä takkia kokeile. = more contrastive, as if saying Try this jacket rather than another one

So for learners, the given order is the safest and most natural one.

You would use the plural imperative:

• Kokeilkaa tätä takkia. = Try this jacket. / Please try this jacket.

So:

• kokeile = say it to one person
• kokeilkaa = say it to several people, or sometimes politely to one person

The dictionary forms are:

• kokeilla = to try
• tämä = this
• takki = jacket / coat

So the sentence is built from:

• kokeilla
• tämä
• takki

but in the actual sentence they appear as:

• kokeile = imperative singular
• tätä takkia = partitive singular

That is a very typical thing in Finnish: the dictionary forms are often quite different from the forms used in real sentences.