Learn Hardcore Japanese: mazimena gakusei ha mainiti tosyokan de benkyousimasu. - Serious students study at the library every day.

な‑adjectives need な when they come directly in front of a noun:
- 真面目な学生 – a serious / diligent student
- 有名な先生 – a famous teacher
When a な‑adjective comes at the end of the sentence describing the subject, you use だ / です, not な:
- 学生は真面目です。 – The student is serious.
- You cannot say 学生は真面目なです。 (✕)

So:

Before a noun: 真面目な学生
As a predicate: 学生は真面目だ / です

What is the difference between 真面目な学生は毎日図書館で勉強します。 and 学生は真面目です。毎日図書館で勉強します。?

They describe similar facts, but the structure and emphasis differ.

真面目な学生は毎日図書館で勉強します。
- Literally: “Serious students study at the library every day.”
- 真面目な学生 is a single noun phrase: “serious students”.
- The sentence focuses on what serious students do.
学生は真面目です。毎日図書館で勉強します。
- “The student(s) is/are serious. (They) study at the library every day.”
- First sentence: describes the character of the student(s).
- Second sentence: adds another fact about them.
- Slightly more explanatory / two-step feeling.

The original single sentence feels smoother and more natural as a general statement about “serious students” and their habit.

What exactly does the particle は do after 学生 here? Could I use が instead?

In 真面目な学生は毎日図書館で勉強します。, は marks the topic:

Literally: “As for serious students, (they) study at the library every day.”
It presents 真面目な学生 as the thing you’re going to talk about.

If you say:

真面目な学生が毎日図書館で勉強します。

then が marks the subject with a nuance like:

“It is the serious students (as opposed to others) who study at the library every day.”
More contrastive or identifying: emphasizing who does the action.

In general:

X は … – “As for X, …” (topic, often more general statement)
X が … – “X is the one that …” (subject, often more specific/new information)

In a generic rule‑like statement, は feels more natural.

Why is there no particle between 真面目な and 学生?

真面目な is directly modifying 学生, just like an adjective before a noun in English:

English: “serious student” (no preposition between “serious” and “student”)
Japanese: 真面目な学生 (no particle between 真面目な and 学生)

Particles appear after whole phrases, not between an adjective and the noun it modifies. So you get:

真面目な学生
- は – “serious students (as for them) …”
大きな図書館
- で – “in the big library …”

Can I move 毎日 to a different position, like 真面目な学生は図書館で毎日勉強します。? Does the meaning change?

You can move 毎日, and the basic meaning stays the same (“every day”). Some common, natural orders:

真面目な学生は毎日図書館で勉強します。
– Very natural. Slight sense of “Every day, they study at the library.”
真面目な学生は図書館で毎日勉強します。
– Also natural. Slight sense of “At the library, they study every day.”
毎日真面目な学生は図書館で勉強します。
– Grammatically okay, but feels a bit unnatural / marked; sounds like “Every day, serious students study at the library,” with more focus on 毎日 as the starting frame.

In Japanese, adverbs like 毎日, よく, たいてい are fairly flexible, but the first version (the original) is the most typical for this kind of sentence.

Why is it 図書館で and not 図書館に before 勉強します?

The choice between で and に is about the role of the place:

で marks the location where an action is performed.
- 図書館で勉強します。 – “(I) study at the library.”
- 学校で働きます。 – “(I) work at school.”
に is usually:
- a destination: 図書館に行きます。 – “(I) go to the library.”
- or a location of existence with いる / ある:
  図書館に学生がいます。 – “There is a student in the library.”

Since 勉強します is an action done at a place, で is correct: the library is the place where the studying happens.

Why doesn’t 勉強します have an object? In English we say “study something”.

In Japanese, 勉強する can be:

Transitive with an object:
- 日本語を勉強します。 – “(I) study Japanese.”
- 歴史を勉強します。 – “(I) study history.”
But also used more like “to study (in general)” with no explicit object:
- 図書館で勉強します。 – “(I) study at the library.” (implied “something”)

The object is often omitted if it’s obvious from context:

If you’re in a Japanese class, 勉強します will be understood as “study Japanese.”
As a habit statement, “Serious students study every day at the library,” you don’t really need to spell out the subject of study.

What is the dictionary (plain) form of 勉強します, and when would I use that instead?

The verb here is:

勉強します – polite non‑past (ます‑form)
Dictionary/plain form: 勉強する

Use:

勉強します
- With people you are not close to
- In formal or neutral polite situations
- In most textbooks’ example sentences
勉強する (plain form)
- With friends and family (casual)
- In inner monologue, notes, headlines, dictionary entries
- When connecting in more complex grammar:
  - 勉強することが好きです。 – “(I) like studying.”

So the sentence in plain casual style would be:

真面目な学生は毎日図書館で勉強する。

Does 勉強します mean “studies” or “will study”? Is this present or future?

Japanese non‑past forms (～する / ～します) cover both:

Present (habit / general truth)
Future

Here, from context (毎日, “every day”), it’s clearly a habitual present:

“Serious students study at the library every day.” (routine)

In another context:

明日図書館で勉強します。
– “(I) will study at the library tomorrow.” (future plan)

Same verb form, interpreted as present or future based on time expressions and context.

Does 学生 mean “a serious student” or “serious students”? How do you know singular vs plural?

Japanese nouns like 学生 do not inherently mark singular or plural. Context decides:

真面目な学生は毎日図書館で勉強します。
→ Most naturally read as a general statement:
“Serious students study at the library every day.”

To make it clearly singular or plural, you can add words:

Clearly one:
- 一人の真面目な学生は毎日図書館で勉強します。
  – “One serious student studies at the library every day.”
- ある真面目な学生は… – “A certain serious student…”
Clearly plural:
- 真面目な学生たちは毎日図書館で勉強します。
  – “Serious students study at the library every day.”
  (たち often emphasizes “as a group,” or specific students you have in mind.)

In the original generic, proverb‑like sentence, reading it as plural “serious students” is the most natural.

What nuance does 真面目 have? Is it just “serious”, or also “hard‑working”, “studious”, etc.?

真面目 (まじめ) covers a range of meanings related to earnestness:

“serious” (not frivolous)
“conscientious”
“diligent / hard‑working”
“honest, upright” (in character)

So 真面目な学生 can suggest:

A student who takes studies seriously
Diligent, follows rules, not messing around much

It is usually positive, like praising someone for being reliable and earnest. It can sometimes feel a bit stiff (like “too serious”) depending on tone and context, but in this sentence it’s simply a compliment.

Could I drop any particles in casual speech, like 真面目な学生毎日図書館で勉強します?

In very casual spoken Japanese, some particles, especially は, are often dropped, but not all.

Natural casual options:

真面目な学生は毎日図書館で勉強する。 (original with は)
真面目な学生、毎日図書館で勉強する。
– Replace は with a pause/comma in speech.

However:

You should not drop で here:
- 図書館で勉強する is needed to show the location of the action.
- 図書館勉強する sounds wrong or at least very unnatural.

So:

Droppable in casual speech: often は, sometimes を when obvious.
Generally not droppable: で, に, が (except in some specific patterns).

Your example 真面目な学生毎日図書館で勉強します is missing a natural break or は after 学生, so it feels off; better is:

真面目な学生は毎日図書館で勉強します。 (normal)
or spoken: 真面目な学生、毎日図書館で勉強します。