Puutteellinen selvitys on liian lyhyt.

They do two different jobs.

• puutteellinen directly modifies the noun selvitys. This is called an attributive adjective: puutteellinen selvitys = an inadequate report/explanation.
• lyhyt comes after on and describes the whole subject. This is called a predicative adjective: is too short.

So the structure is:

[puutteellinen selvitys] + on + liian lyhyt
[subject] + is + too short

In Finnish, adjectives usually come before the noun when they directly describe it, just like in English.

• puutteellinen selvitys = inadequate explanation/report
• lyhyt kirja = short book
• suuri talo = big house

So puutteellinen is placed before selvitys because it is part of the noun phrase.

Because puutteellinen selvitys is the subject of the sentence, and subjects are very often in the nominative case.

Here both words are:

• singular
• nominative

Also, in Finnish, an adjective that comes before a noun usually agrees with that noun in case and number.

So:

• puutteellinen = nominative singular adjective
• selvitys = nominative singular noun

They match.

Because it is a predicate adjective after olla (to be).

In a basic sentence like this, the adjective after on is typically in the nominative, and it matches the subject in number:

• Selvitys on lyhyt. = The report is short.
• Selvitykset ovat lyhyet. = The reports are short.

So since the subject is singular (puutteellinen selvitys), lyhyt is singular too.

On is the third-person singular present tense of olla, which means to be.

So:

• minä olen = I am
• sinä olet = you are
• hän on = he/she is
• se on = it is

In this sentence, on means is.

Liian means too.

It is an adverb, and here it modifies the adjective lyhyt:

• lyhyt = short
• liian lyhyt = too short

This is the normal word order in Finnish:

• liian suuri = too big
• liian kallis = too expensive
• liian pitkä = too long

So liian lyhyt is the natural way to say too short.

Because Finnish does not have articles.

English needs words like a and the, but Finnish usually does not mark that distinction directly.

So puutteellinen selvitys could mean, depending on context:

• an inadequate report
• the inadequate report
• sometimes just inadequate report in a more general sense

Context tells you which is meant.

-nen is a very common Finnish ending, especially in adjectives and some nouns.

In puutteellinen, it is simply part of the word. You do not translate -nen by itself here; the whole word means inadequate, deficient, or insufficient depending on context.

A useful thing to know is that -nen words often change their stem when inflected:

• nominative: puutteellinen
• other forms use the stem puutteellise-

For example:

• puutteellisessa selvityksessä = in an inadequate report/explanation

So even though the dictionary form ends in -nen, the stem often becomes -se- or -ise- in other forms.

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

Puutteellinen selvitys on liian lyhyt.

This is a normal subject + verb + complement sentence.

You can move things around for emphasis, but it may sound marked or literary. For example:

• Liian lyhyt on puutteellinen selvitys.

This is understandable, but much less neutral.

So for learners, the safest default is:

• subject
• olla
• predicate

You should usually think of puutteellinen selvitys as one noun phrase:

• puutteellinen = inadequate
• selvitys = report/explanation/account
• together: an inadequate report/explanation

Then the sentence says something about that whole thing:

• Puutteellinen selvitys = the subject
• on liian lyhyt = what is being said about it

So it is helpful to chunk the sentence like this:

[Puutteellinen selvitys] [on] [liian lyhyt].