kore ha tadasii handan desita.

A natural breakdown is:

• これ = this
• は = topic marker
• 正しい = correct / right
• 判断 = judgment / decision
• でした = was (polite past form of です)

So the sentence structure is basically:

• これ
  • は = as for this
• 正しい判断 = a correct judgment / the right decision
• でした = was

So the whole sentence means something like This was the right decision or This was a correct judgment.

は marks the topic of the sentence.

In これは正しい判断でした, the speaker is saying something about これ, meaning this. So これ is the thing being discussed.

You can think of it as:

• As for this, it was the right decision.

This does not always match English word-for-word. In English we just say This was the right decision, but in Japanese the topic marker は is doing important grammatical work.

This is one of the first things Japanese learners notice.

When は is used as a particle, it is pronounced wa, not ha.

So:

• これは is pronounced kore wa
• not kore ha

But when は is part of a word, it is usually pronounced ha.

Because 正しい is an i-adjective, and in Japanese, an i-adjective can directly modify a noun.

So:

• 正しい判断 = correct judgment

No extra word is needed between them.

This is similar to:

• 大きい犬 = big dog
• 新しい本 = new book
• 正しい答え = correct answer

So 正しい directly describes 判断.

判断 literally means judgment, assessment, or decision depending on context.

In this sentence, English might translate it as:

• judgment
• decision
• call

The nuance is that 判断 often suggests a mental judgment or evaluation, not just choosing something at random.

So 正しい判断でした has the feeling of:

• It was the right judgment
• That was the correct call
• It was the right decision

でした is the polite past form of です.

So:

• です = is / am / are
• でした = was / were

That means the sentence is talking about something as a completed or past situation:

• これは正しい判断です。 = This is the right decision.
• これは正しい判断でした。 = This was the right decision.

The speaker is looking back on it.

Because in this sentence, 正しい is modifying the noun 判断.

The predicate of the sentence is not 正しい by itself. The predicate is the noun phrase 正しい判断, followed by でした.

So the structure is:

• これは
  • 正しい判断
    • でした
• As for this, it was a correct judgment

If you say 正しかった, then 正しい becomes the predicate itself:

• これは正しかった。 = This was correct.

That is a different structure. It does not explicitly say judgment/decision.

Yes, but it means something slightly different.

• これは正しいです。 = This is correct.
• これは正しい判断でした。 = This was the correct judgment / the right decision.

The second sentence is more specific because it includes 判断.

So:

• 正しいです talks about something being correct.
• 正しい判断でした talks about something being a correct judgment.

これ means this by itself.

この must be followed by a noun.

So:

• これ = this
• この判断 = this judgment
• この決定 = this decision

In your sentence, これ stands alone as the topic:

• これは正しい判断でした。

If you wanted to use この, you would need a noun after it, for example:

• この判断は正しかったです。 = This judgment was correct.

Yes, in a way.

Japanese often leaves out things that English requires. English usually needs a subject like this or it, but Japanese often relies on context.

Here, これ is the topic, and English naturally turns that into the subject:

• This was the right decision.

So there is no extra spoken word for it in Japanese. The sentence is already complete as it is.

The plain form is:

• これは正しい判断だった。

Here:

• でした = polite past
• だった = plain past

So:

• これは正しい判断でした。 = polite
• これは正しい判断だった。 = plain / casual

Both mean basically the same thing, but the politeness level is different.

It is read:

• これ は ただしい はんだん でした
• Romanized: kore wa tadashii handan deshita

A few important points:

• は is pronounced wa
• 正しい is ただしい
• 判断 is はんだん

So the full pronunciation is:

• kore wa tadashii handan deshita

Japanese does not normally use articles like a, an, or the.

So 正しい判断 could mean:

• a correct judgment
• the correct judgment
• the right decision

Which one sounds best depends on context and translation style.

That is completely normal in Japanese. The listener understands from the situation what is meant.