Learn Hardcore Japanese: benkyou ni ha, syuutyuuryoku ga daizi da to omoimasu. - I think concentration is important for studying.

勉強は難しいです。
As for studying, it is difficult.
勉強には集中力が大事だと思います。
For studying / When it comes to studying, concentration is important (I think).

Why is 集中力 marked with が? Could we use は instead?

The pattern here is:

X には Y が大事だ。
For X, Y is important.

勉強には → “for studying / when it comes to studying” (context)
集中力が → marks what is important in that context (the subject)
大事だ → is important

Using が on 集中力 fits the pattern “Xには Yが …”, where Y is the thing that is important/necessary/valuable for X.

You can say 集中力は instead, but the nuance changes:

勉強には集中力が大事だ。
For studying, concentration is (what’s) important.
→ Neutral “Y is important for X.”
勉強には集中力は大事だ。
This sounds more contrastive, like: At least as far as studying goes, concentration is important (maybe other things aren’t, or we’re contrasting with something else).

So が here is natural and neutral, and fits the common structure XにはYが大事だ.

What exactly does 集中力 mean? Is it just “concentration”?

集中力 (shūchūryoku) is:

集 – gather
中 – middle / focus
力 – power / ability

So literally, it’s the ability/power to concentrate or focus.

Nuance:

It’s not just the act of concentrating at one moment.
It’s more like your capacity to stay focused, your mental focusing ability.

In English, it’s usually translated as:

concentration (ability)
power of concentration
ability to focus

So 勉強には集中力が大事だ is about the importance of having that ability, not just concentrating once.

Why is it 大事だと思います and not 大事ですと思います?

Before verbs like 思う (to think), 言う (to say), etc., the clause that comes with と is almost always in plain form, not polite です/ます form.

So we have:

大事だ (plain copula) + と
- 思います (polite)
→ 大事だと思います (correct and natural)

大事ですと思います is generally ungrammatical / very unnatural.
You don’t mix です directly before と in this pattern.

Correct patterns:

Plain + 思う
- 大事だと思う。 (casual)
Plain + 思います
- 大事だと思います。 (polite)

But 大事ですと思います → avoid this.

What is the role of と before 思います? Why do we need it?

The と here is the quotative particle.

It marks the content of what is thought/said/felt, similar to “that …” or quotation marks in English.

Structure:

[勉強には集中力が大事だ] と思います。
I think *that [concentration is important for studying].*

So:

と attaches to the whole clause 勉強には集中力が大事だ
思います is the main verb: “I think”

You use と like this with many verbs:

〜と思う – think that …
〜と言う – say that …
〜と感じる – feel that …
〜と信じている – believe that …

Could we drop と思います and just say 勉強には集中力が大事です? What would be the difference?

Yes, you can say:

勉強には集中力が大事です。
Concentration is important for studying.

Difference in nuance:

With 思います – 勉強には集中力が大事だと思います。
- Literally: I think concentration is important for studying.
- Sounds softer, more subjective.
- Common in Japanese to soften opinions and avoid sounding too direct or absolute.
- Polite and modest tone.
Without 思います – 勉強には集中力が大事です。
- More like a plain statement of fact.
- Can sound more assertive / objective, as if it’s just the way things are.
- Still polite because of です, just less “hedged.”

In everyday polite conversation, Japanese speakers often use 〜と思います to keep their statements from sounding too strong.

Why is 勉強 used without する here? Is 勉強 a noun or a verb?

勉強 (benkyou) is originally a noun meaning “study / studying.”

It can combine with する to make a verb:

勉強する – to study

But as a noun, 勉強 can already be used with particles:

勉強が好きです。 – I like studying.
勉強の時間。 – Study time.
勉強には〜 – For studying …

In 勉強には, we are using 勉強 as a noun:

勉強に – for study / for studying
Then は makes it the topic: 勉強には

So you don’t need する here because you’re not saying “to study,” you’re talking about the activity of studying in general.

Can we say 勉強するには、集中力が大事だと思います instead? Does it change the meaning?

Yes, this is grammatical and natural:

勉強するには、集中力が大事だと思います。

Nuance:

勉強には
→ For studying (as an activity in general)
Very general: “In the realm of study, concentration is important.”
勉強するには
→ In order to study / When you study
Emphasizes the act of doing the studying. It feels a bit more concrete: “If you want to study / when you go to study, concentration is important.”

Both are close in meaning, but 勉強するには focuses slightly more on actually performing the action.

Are 大事, 大切, and 重要 all the same? Why use 大事 here?

All three can be translated as “important,” but their typical usage/nuance differs:

大事 (daiji)
- Very common in speech.
- “Important,” “valuable,” sometimes “precious.”
- Can be emotional or practical.
- E.g. 健康が大事です。 – Health is important.
大切 (taisetsu)
- “Important” with a stronger sense of cherishing / caring about.
- Often used for things you value emotionally: people, relationships, memories.
- E.g. 家族はとても大切です。 – Family is very important/precious.
重要 (jūyō)
- More formal / academic / technical.
- “Significant,” “crucial.”
- Common in documents, news, business, exams.
- E.g. これは重要な問題です。 – This is an important issue.

In 勉強には集中力が大事だと思います, 大事 sounds:

Natural and conversational.
Neither too emotional nor too formal.
Fits well with a general opinion about study.

You could also say:

勉強には集中力が大切だと思います。 (slightly more “valuing” tone)
勉強には集中力が重要だと思います。 (more formal/serious)

But 大事 is the most neutral, everyday choice here.

Is the word order fixed? Could we say 集中力が勉強には大事だと思います or 集中力は勉強に大事だと思います?

Word order in Japanese is somewhat flexible, but not every permutation sounds natural.

Original:
- 勉強には集中力が大事だと思います。
  → Very natural.
  Pattern: Xには Yが大事だ = “Y is important for X.”
集中力が勉強には大事だと思います。
- This is grammatical and can be used.
- The focus slightly shifts toward 集中力 (“As for concentration, it is important for studying”).
- Feels a bit like you’re talking about concentration and then specifying for what it is important.
集中力は勉強に大事だと思います。
- This sounds off / unnatural to many native speakers.
- The pattern Xに大事だ is unusual; we typically say XにはYが大事だ.
- If you really want 集中力は, a more natural version is:
  - 集中力は勉強にとって大事だと思います。
    (Concentration is important for studying. – using 〜にとって “for / to (someone/something)”)

So the most natural simple pattern is:

勉強には集中力が大事だと思います。

Other variations exist, but you should be careful to keep the common structural pattern XにはYが大事だ for “Y is important for X.”