Learn Hardcore Japanese: hito ni yotte nihongo no benkyou no kanzikata ha tigaimasu. - The way people feel about studying Japanese is different from person to person.

Noun + によって often means:
- “depending on ~” / “according to ~” / “by ~ (as a factor)”
In this sentence, 人によって means:
- “depending on the person” / “from person to person”

So:

人によって　…　違います。
→ “It’s different depending on the person.”

This is different from:

人にとって　…
which usually means “for (someone), from (someone’s) point of view,” as in:
- あなたにとって日本語は難しいですか。
  “Is Japanese difficult for you?”

Here we’re not saying “for a person” but “depending on which person,” so によって is the correct one.

Why is there no particle after 人? Why not 人は or 人が?

人 and によって form one chunk: 人によって.

Think of によって as a postposition-like piece that directly attaches to a noun.
So the structure is:
- 人 (person) + によって (depending on) → 人によって (“depending on the person”)

If you added は or が after 人, you’d be breaking that set expression.
You want:

人によって (correct)
not
人はによって or 人がによって (unnatural)

What does 日本語の勉強の感じ方 literally mean, and why are there two の?

Break it down from the right:

感じ方
- From verb 感じる (“to feel”) + 方 (“way, manner, method”)
  → 感じ方 = “way of feeling,” “how something feels,” “how one feels something”
勉強の感じ方
- 勉強 = study, studying
- 勉強の感じ方 = “the way (someone) feels about studying,”
  or “the way studying feels”
日本語の勉強の感じ方
- 日本語の勉強 = “study of Japanese,” “Japanese study”
- Add の感じ方:
  → 日本語の勉強の感じ方 =
  “the way (someone) feels about studying Japanese” /
  “the way studying Japanese feels (to them)”

Each の links one noun to the next:

日本語の勉強 (study of Japanese)
勉強の感じ方 (way of feeling about study)

Japanese often chains several Noun + の + Noun like this; it’s very common and natural.

What exactly is 感じ方 grammatically? Is 方 a separate word?

Yes, 方 (かた) is a separate word here.

Pattern: Verb (ます-stem) + 方
→ “the way/method of doing (that verb)”

Examples:

読む → 読み方 = “way of reading,” “pronunciation” (in some contexts)
書く → 書き方 = “way of writing,” “how to write”
感じる → 感じ方 = “way of feeling,” “how (someone) feels something”

So 感じ方 is a noun formed from the verb 感じる.
In this sentence, 感じ方 functions as the topic (marked by は).

Why is は attached to 感じ方 (感じ方は) instead of to 人 or something else?

は marks the topic—what the sentence is “about.”

Here, the sentence is structured as:

(人によって) 日本語の勉強の感じ方は違います。

So, literally:

“As for the way of feeling about studying Japanese, (it) is different depending on the person.”

Putting は after 感じ方 emphasizes:

“When we talk about the way it feels to study Japanese, that way differs from person to person.”

You could imagine:

人によっては、日本語の勉強の感じ方が違います。

where 人によっては is a topical phrase and 感じ方が is the subject—but that slightly shifts the focus.
In the original, the main topic is the 感じ方, not “people.”

Could I change 感じ方は違います to 感じ方が違います? What would be the difference?

Yes, 日本語の勉強の感じ方が違います is grammatically fine.

Nuance:

感じ方は違います。
→ は = topic marker.
Focus: “Speaking of the way it feels to study Japanese, (that) is different depending on the person.”
It feels like a general comment or explanation.
感じ方が違います。
→ が = subject marker (more “who/what is doing/being”).
Focus: “It’s the way of feeling that is (what’s) different.”
Slightly more contrastive or specific, like picking out what is different.

In many contexts, especially in spoken Japanese, both are acceptable and the difference is subtle.
The version with は just sounds a little more like a general statement about that topic.

Why is there no を-object? Isn’t 違います a verb that should take an object?

違います (plain form 違う) works differently from an English “to differ (from).”

Common patterns:

A は B と違います。
- “A is different from B.”
A が違います。
- “A is wrong / A is not the one / A is different.”

In this sentence:

There’s no explicit “B” to compare to; we’re saying “(things) differ” in general.
違います here is closer to “(they) are different / vary.”

The implied structure is something like:

人によって、日本語の勉強の感じ方は（人ごとに）違います。
“Depending on the person, each person’s way of feeling about studying Japanese is different.”

So there is no を because we don’t have a direct object; we just have something that is different.

Is “the subject” of the sentence 人 or 日本語の勉強の感じ方?

Grammatically, the topic (and effectively the main “subject” in English terms) is:

日本語の勉強の感じ方 (marked by は)

人によって is an adverbial phrase:

It modifies the whole predicate 違います and tells you in what way / under what factor the topic is different.
So the structure is:
- [人によって] [日本語の勉強の感じ方は] 違います。
  “Depending on the person, the way one feels about studying Japanese is different.”

So:

Main topic: 日本語の勉強の感じ方
Condition/factor: 人によって
Predicate: 違います

What level of politeness is 違います compared with 違う?

違う = plain form (“dictionary form”)
Used in:
- casual speech
- informal writing
- plain-style narrative
違います = polite (ます-form)
Used in:
- talking to people you’re not close with
- conversations with teachers, colleagues, customers
- most textbooks’ model sentences

So this sentence is in the polite style (です・ます style), appropriate for neutral/formal contexts:

人によって日本語の勉強の感じ方は違います。
sounds like something a teacher might say in class.

Are there other natural ways to express the same idea, and do they change the nuance?

Yes, several:

人によって、日本語の勉強の感じ方が違います。
- Uses が instead of は.
- Slightly more like “what’s different is the way it feels,” but the core meaning is the same.
人によって、日本語の勉強の感じ方は異なります。
- 異なります is a bit more formal/literary than 違います.
- Feels more like written language, explanations, articles, etc.
人によって、日本語の勉強の感じ方が変わります。
- 変わります = “changes/varies.”
- Emphasizes variation rather than “being different” in a contrastive sense.

All of these can convey roughly the same meaning as the original sentence; the differences are mainly in formality and nuance of “different” vs “varies.”