Słońce szkodzi jedwabiowi.

Because szkodzić requires the dative case.

The dictionary form jedwab means silk, but after szkodzić you do not use the accusative like you often would in English. Instead, Polish treats the thing affected as an indirect object:

• szkodzić komu? czemu? = to harm whom? what? in the dative

So:

• jedwab = nominative
• jedwabiowi = dative singular

That is why Słońce szkodzi jedwabiowi is grammatically correct.

Yes, normally it does.

You say:

• szkodzić komuś / czemuś = to be harmful to someone / something

Examples:

• Dym szkodzi zdrowiu. = Smoke harms health.
• Hałas szkodzi uszom. = Noise harms the ears.
• To szkodzi dzieciom. = That is harmful to children.

So in your sentence, jedwabiowi is in the dative because szkodzić requires it.

Słońce is in the nominative singular, because it is the subject of the sentence.

It is the thing doing the harming:

• Słońce = the sun
• szkodzi = harms / is harmful
• jedwabiowi = to silk

Also, słońce is a neuter noun, which is why in the singular it often goes with neuter verb agreement in past tense, though in the present tense szkodzi looks the same for all genders.

Szkodzi is the 3rd person singular present tense of szkodzić.

So it means:

• he harms
• she harms
• it harms
• or more naturally here, is harmful to

Conjugation:

• ja szkodzę = I harm
• ty szkodzisz = you harm
• on/ona/ono szkodzi = he/she/it harms
• my szkodzimy = we harm
• wy szkodzicie = you (plural) harm
• oni/one szkodzą = they harm

In this sentence, słońce is singular, so the verb is szkodzi.

Because the sentence expresses a general truth or regular fact.

Polish often uses the present tense for things that are generally true:

• Cukier szkodzi zębom. = Sugar harms teeth.
• Słońce szkodzi jedwabiowi. = The sun harms silk.

It does not mean only right now at this moment. It means something like sunlight is bad for silk in general.

Not always exactly. In many contexts, szkodzić means:

• to harm
• to be harmful to
• to be bad for

So Słońce szkodzi jedwabiowi can sound very natural in English as:

• The sun harms silk
• Sunlight is harmful to silk
• The sun is bad for silk

Polish often uses szkodzić where English might prefer be harmful to.

Yes. Polish word order is more flexible than English because the case endings show the grammatical roles.

The neutral order here is:

• Słońce szkodzi jedwabiowi.

But you could also say:

• Jedwabiowi szkodzi słońce.

This would put more emphasis on jedwabiowi.

Even though the order changes, the endings still show that:

• słońce is the subject
• jedwabiowi is the dative object

So the meaning stays basically the same, though the emphasis changes.

Because Polish has no articles like English a/an/the.

So słońce can mean:

• sun
• the sun

And jedwab can mean:

• silk
• the silk

You understand which one is meant from context. In a general statement like this, English often uses the sun and just silk.

A rough pronunciation guide is:

• Słońce ≈ SWON-tseh
• szkodzi ≈ SHKO-djee
• jedwabiowi ≈ yed-vah-BYOH-vee

A few useful notes:

• sz sounds like English sh
• cz sounds like English ch, but here you have ńc, so słońce is a bit softer
• ł sounds like English w
• dzi sounds like a soft j / dj
• je- at the start sounds like ye-

The stress is usually on the second-to-last syllable:

• słońCE
• szkoDZI
• jedwaBIOwi

Because that is a common dative singular ending for many masculine nouns.

The noun jedwab is masculine, and in the dative singular it becomes:

• jedwab → jedwabiowi

This pattern appears in many masculine nouns:

• student → studentowi
• kot → kotu or sometimes other patterns depending on the noun
• chłopiec → chłopcu
• mąż → mężowi

So -owi is one of the standard dative singular endings for masculine nouns, though not the only one.

Yes. Szkodzić is imperfective.

That fits this sentence well, because the sentence describes a general ongoing fact. The perfective partner is usually zaszkodzić, which is more like to do harm, to have a harmful effect, often in a more single-event sense.

Compare:

• Słońce szkodzi jedwabiowi. = The sun is harmful to silk. / Sun harms silk.

  • general truth, habitual, imperfective

• To może zaszkodzić jedwabiowi. = That may damage / harm the silk.

  • more like a single harmful result, perfective

So szkodzić is the natural choice here.

No. That would be ungrammatical.

After szkodzić, you need the dative, not the nominative or accusative. So you must say:

• Słońce szkodzi jedwabiowi.

Using jedwab would ignore the case required by the verb.

This is one of those important verb patterns that you simply have to learn:

• pomagać komuś/czemuś = to help someone/something
• przeszkadzać komuś/czemuś = to disturb someone/something
• szkodzić komuś/czemuś = to harm someone/something

All of these take the dative.