Questo errore sembra ovvio.

Sembra is the third-person singular present tense of sembrare, which means to seem.

It is third-person singular because the subject is questo errore, which is singular:

• questo errore sembra
• questi errori sembrano

So the form of the verb changes to match the subject.

Because they both refer to errore, and errore is a masculine singular noun.

In Italian, words that describe or point to a noun usually agree with it in gender and number:

• questo errore ovvio → masculine singular
• questa situazione ovvia → feminine singular
• questi errori ovvi → masculine plural
• queste cose ovvie → feminine plural

So in Questo errore sembra ovvio, both questo and ovvio match errore.

That is a very common question. In Italian, nouns ending in -e can be either masculine or feminine, so the ending alone does not tell you the gender.

You usually need to learn the gender together with the noun:

• l'errore → masculine
• un errore → masculine

So errore is simply one of those -e nouns whose gender must be memorized.

Because questo is a demonstrative adjective (this), and in Italian it normally takes the place of the article.

So you say:

• questo errore = this error / this mistake

not:

• il questo errore ✗

This works like English: you say this mistake, not the this mistake.

Because the sentence is built with a linking verb: sembrare.

In Questo errore sembra ovvio, ovvio is not simply attached to the noun inside the noun phrase. Instead, it is describing the subject through the verb sembra.

So the structure is:

• subject
  • linking verb
    • adjective

That is similar to English:

• This mistake seems obvious

If you want to make obvious part of the noun phrase itself, you would use a different structure, for example:

• Questo è un errore ovvio = This is an obvious mistake

Because after sembrare, you normally use an adjective, not an adverb.

• ovvio = obvious → adjective
• ovviamente = obviously → adverb

Here, ovvio describes errore, so it must be an adjective:

• Questo errore sembra ovvio.

If you used ovviamente, you would be modifying the whole statement instead:

• Ovviamente, questo è un errore. = Obviously, this is a mistake.

The difference is the same basic one as in English between seems obvious and is obvious.

• sembra ovvio = softer, more tentative, based on appearance or impression
• è ovvio = stronger, more direct, more definite

So:

• Questo errore sembra ovvio can sound a bit more cautious
• Questo errore è ovvio is more blunt and certain

Using sembra often makes the sentence sound less absolute.

It can mean both, depending on context.

For an English speaker, errore often overlaps with:

• error
• mistake

In everyday Italian, errore is very common in situations where English might choose either word.

For example, it can be used for:

• a wrong answer
• a typo
• a bad decision
• a technical error

So the best English translation depends on context, not on a strict one-word rule.

Yes, but the basic order in this sentence is the most natural and neutral:

• Questo errore sembra ovvio.

Italian does allow word-order changes, but they usually add emphasis, contrast, or a more literary tone.

For a learner, the safest pattern is:

• subject
  • verb
    • adjective/complement

So this sentence is a very standard model to follow.