nou ha daizi desu.

It is read:

のう は だいじ です
Romanized: nō wa daiji desu

A few notes:

• 脳 = のう (nō) = brain
• The particle は is written ha but pronounced wa here.
• 大事 = だいじ (daiji)
• です = desu

So the full sentence sounds like:

Nō wa daiji desu.

This is one of the first things learners notice in Japanese.

When は is used as a particle marking the topic of the sentence, it is pronounced wa, not ha.

So in:

脳 は 大事 です。

the は is the topic marker, so you say wa.

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

Example:

• はな = flower or nose, depending on kanji/context, pronounced hana

は marks the topic of the sentence.

So 脳は means something like:

• as for the brain
• speaking of the brain
• the brain, ...

Then the rest of the sentence says something about that topic:

• 大事です = is important

So the whole sentence is literally close to:

As for the brain, it is important.

Natural English: The brain is important.

Great beginner question. Both は and が can sometimes look like they translate to an English subject, but they do different jobs.

In this sentence, は is used because 脳 is being presented as the topic.

• 脳は大事です。
  As for the brain, it is important.

This feels general, explanatory, or contrastive depending on context.

If you said:

• 脳が大事です。

it would sound more like the brain is the important one or it’s the brain that is important, depending on context. It can feel more focused or contrastive.

For a simple general statement like The brain is important, は is the most natural choice.

大事 usually means:

• important
• valuable
• precious
• something that should be taken care of

So in this sentence, 脳は大事です means the brain is important, but it can also carry the nuance that the brain is something valuable and worth caring about.

A very common related expression is:

• お体は大事にしてください。
  Please take care of yourself / your health.

So 大事 is not just abstract importance; it often has a sense of care and value too.

In this sentence, 大事 behaves like a na-adjective.

That means it can be used with です to describe something:

• 脳は大事です。 = The brain is important.

Before a noun, it usually takes な:

• 大事なもの = an important thing
• 大事な人 = an important person

So:

• predicative use: 大事です
• before a noun: 大事な + noun

です is a polite sentence ending that makes the statement sound neutral and polite.

So:

• 脳は大事です。 = polite
• 脳は大事だ。 = plain style
• 脳は大事。 = very casual / conversational

In beginner materials, です is very common because it is safe and polite in many situations.

It does not mean exactly the same thing as English is in every situation, but in this sentence it helps form the polite statement is important.

Yes.

• 脳は大事です。 = polite
• 脳は大事だ。 = plain / less polite
• 脳は大事。 = casual

The meaning is basically the same, but the style changes.

Use です when speaking politely, especially with people you do not know well, teachers, coworkers, or in formal situations.

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

So 脳 can mean:

• a brain
• the brain
• brains in some contexts

The exact meaning comes from context.

In 脳は大事です, the most natural English translation is The brain is important or Brains are important, depending on the situation. If the intended meaning has already been shown to the learner, that context decides which English version fits best.

Japanese often puts the main statement at the end.

Here the structure is:

• 脳は = topic
• 大事です = is important

So the pattern is roughly:

Topic + comment

This is very common in Japanese.

English:

• The brain is important.

Japanese:

• Brain + topic marker + important + polite ending

So yes, this word order is very natural in Japanese.

Yes, depending on context.

Japanese nouns usually do not mark singular vs. plural the way English does. So 脳 by itself does not automatically tell you whether it is:

• the brain
• a brain
• brains

In many contexts, 脳は大事です would be understood as a general statement like:

• The brain is important.
• Brains are important.

The surrounding context tells you which English wording sounds best.

Yes, 脳 and 頭 are different.

• 脳（のう） = brain
• 頭（あたま） = head

So:

• 頭が痛い = My head hurts
• 脳が大事 = The brain is important

In everyday conversation, 頭 is much more common because people often talk about the head, headaches, being smart, and so on. 脳 is more specifically the physical brain, and often appears in medical, scientific, educational, or serious contexts.

Normally, standard Japanese writing does not use spaces between words.

So the natural written form is:

脳は大事です。

Spaces are sometimes added in beginner materials to make the sentence easier to read, but in real Japanese text they are usually omitted.