Voin kuvata yhden vahvuuden ja yhden heikkouden sekä perustella molemmat.

Voin is the 1st person singular form of voida, meaning can / am able to.

So:

• voida = to be able to, can
• voin = I can

Finnish usually leaves out the subject pronoun minä because the verb ending already shows who the subject is. So Voin by itself already means I can.

Because after voida, Finnish uses the 1st infinitive, which is the dictionary form of the verb.

So:

• voin kuvata = I can describe
• not voin kuvaan

This is the normal pattern with modal verbs in Finnish:

• voin tehdä = I can do
• haluan mennä = I want to go
• saan puhua = I may / get to speak

Here both kuvata and perustella are infinitives controlled by voin.

Yes, kuvata can mean both to describe and to photograph / film, depending on context.

In this sentence, because the objects are vahvuus and heikkous, it clearly means to describe.

Examples:

• kuvata henkilöä can mean describe a person
• kuvata elokuvaa can mean film a movie

So the context tells you which meaning is intended.

Because they are singular total objects.

In Finnish, when the object is seen as a complete whole, a singular object often appears in the genitive-looking object form:

• yhden vahvuuden
• yhden heikkouden

Here the idea is one complete strength and one complete weakness, so the object is not partitive.

A useful contrast:

• kuvata yhden vahvuuden = describe one whole strength
• kuvata vahvuutta = describe strength / some aspect of a strength

So the -n form here signals a complete, countable object.

Because Finnish makes it explicit that there is one of each:

• yhden vahvuuden = one strength
• yhden heikkouden = one weakness

Repeating yhden keeps the structure clear and balanced. It matches the English idea one strength and one weakness, not just one strength and weakness.

They mean:

• vahvuus = strength, strong point
• heikkous = weakness, weak point

Both are common abstract nouns, and they are often used when talking about:

• personal qualities
• arguments
• products
• plans
• applications
• essays

So this sentence could fit many contexts, such as an interview, a presentation, or an exam answer.

Both are conjunctions meaning and, but they are used a little differently.

In this sentence:

• ja joins the two noun phrases: yhden vahvuuden ja yhden heikkouden
• sekä joins the second action to the first: kuvata ... sekä perustella ...

Sekä often sounds a bit more formal, careful, or written than plain ja.

So this sentence sounds slightly polished or academic. In everyday speech, many people would simply use ja there too:

• Voin kuvata yhden vahvuuden ja yhden heikkouden ja perustella molemmat.

That is also correct.

Because molemmat is a plural total object here.

It refers to the two things already mentioned:

• the strength
• the weakness

The meaning is justify both of them completely, so Finnish uses the nominative plural form molemmat.

Compare:

• perustella molemmat = justify both, as complete items
• perustella molempia = would suggest a partitive meaning, which does not fit as naturally here

So molemmat is the expected form.

Because Finnish can let one modal verb govern more than one infinitive.

The structure is basically:

• Voin
  
  • kuvata yhden vahvuuden ja yhden heikkouden
  • sekä perustella molemmat

So the meaning is:

• I can describe ... and justify ...

You do not need to repeat voin before perustella, although you could in some contexts for extra emphasis.

Because Finnish often drops personal pronouns when they are not needed.

The verb ending in voin already tells you the subject is I. So:

• Voin = I can
• Minä voin = I can

Adding minä is possible, but it usually adds emphasis, contrast, or clarity.

For example:

• Minä voin, mutta hän ei voi. = I can, but he/she cannot.

In your sentence, no pronoun is needed.

Yes. Finnish word order is fairly flexible, although some versions sound more natural than others.

The given sentence is very natural because it presents the actions in a logical order:

1. describe
2. justify

You could rearrange parts for emphasis, but the focus would change. For example:

• Yhden vahvuuden ja yhden heikkouden voin kuvata sekä perustella molemmat.

This is still understandable, but it sounds more marked.

So the original order is a good neutral choice.

Yes. A very natural alternative is:

• Voin kuvata yhden vahvuuden ja yhden heikkouden ja perustella molemmat.

That version is more conversational and less formal.

The original with sekä sounds a bit more:

• polished
• structured
• written
• formal

So both are correct; the choice is mostly about style.

Yes: perustella means to justify, to give reasons for, or to argue for something.

It is a very useful academic and professional verb in Finnish. You often see it in tasks where someone must not just say something, but also explain why.

For example:

• Perustele vastauksesi. = Justify your answer.
• Voitko perustella mielipiteesi? = Can you justify your opinion?

So in this sentence, kuvata gives the points, and perustella means giving reasons for them.