Learn Hardcore Japanese: sensei ha muzukasii bunpou wo wakariyasui hyougen de setumeisite kuremasu. - The teacher explains difficult grammar using easy-to-understand expressions.

先生は ≈ “As for the teacher,” / “The teacher (on the other hand)...”
It sets 先生 as what we’re talking about, and the rest of the sentence is information about that topic.

If you said 先生が難しい文法を分かりやすい表現で説明してくれます, it would be more like:

“It is the teacher who explains difficult grammar in easy-to-understand terms (for me).”
→ Focus on who does it (contrastive/identifying subject).

In this sentence, we’re just describing what the teacher does in general, so 先生は as a topic (“the teacher”) is more natural.

Why is it 難しい文法を and not something like 文法は難しい?

Here 難しい is directly modifying 文法 like an adjective before a noun in English:

難しい文法 = “difficult grammar”

Grammar point:

Adjectives in the form …い (like 難しい) can go directly before a noun:
- 難しい文法 = difficult grammar
- おいしいりんご = delicious apple

Compare:

難しい文法を説明してくれます。
“(He/She) explains difficult grammar.”
→ “Difficult” is part of the noun phrase.
文法は難しいです。
“Grammar is difficult.”
→ Here grammar is the topic/subject and difficult is the predicate.

So the original sentence is not saying “Grammar is difficult”; it’s selecting a type of grammar (the difficult kind) as the object being explained.

What exactly does 分かりやすい mean, and how is it formed?

分かりやすい (わかりやすい) is an い-adjective meaning “easy to understand,” “understandable,” or “clear.”

It’s formed from:

Verb 分かる (“to understand”)
- the helper adjective 〜やすい, which means “easy to V”

Pattern:

Vます-stem + やすい = easy to do V
- 分かる → 分かり + やすい → 分かりやすい = easy to understand
- 見る → 見 + やすい → 見やすい = easy to see
- 使う → 使い + やすい → 使いやすい = easy to use

Once formed, 分かりやすい behaves as a normal い-adjective:

分かりやすい表現 = easy-to-understand expressions
分かりやすい説明 = easy-to-understand explanation

What does で mean in 分かりやすい表現で? Why use で and not を or に?

In 分かりやすい表現で, the particle で indicates means / method / manner:

分かりやすい表現で説明してくれます
= “(He/She) explains using easy-to-understand expressions/phrasing.”

Here are some typical uses of で:

Means / tool
- ペンで書きます。= I write with a pen.
- 日本語で話します。= I speak in Japanese.
- 分かりやすい表現で説明します。= I explain in easy-to-understand terms.
Place where an action happens
- 学校で勉強します。= I study at school.

In this sentence, で is not marking the direct object; that’s 難しい文法を.
The teacher:

explains (説明してくれます)
what? difficult grammar (難しい文法を)
how / by what means? in easy-to-understand expressions (分かりやすい表現で)

Why is it 説明してくれます instead of just 説明します? What does 〜てくれる do?

The pattern Vて + くれる expresses that someone does something for me / for us (the speaker’s side). It’s called a benefactive construction.

説明します = “(He/She) explains.”
説明してくれます = “(He/She) explains (for me / for us).”
→ It adds the nuance that this action is helpful/beneficial to the speaker.

General pattern:

(Person) が (someone on my side) に Vてくれる
= (Person) kindly does V for (someone on my side).

Examples:

友だちが宿題を手伝ってくれました。
= My friend helped me with my homework (for my benefit).

In the original sentence, くれます makes it sound like:

“The teacher kindly explains difficult grammar to us in easy-to-understand terms.”

If you say 説明します without くれる, it’s more neutral; it just states what the teacher does, without highlighting that it benefits you.

There is no 私に in the sentence, but we still translate it as “for me/us.” Who is くれる for?

With 〜てくれる, if no indirect object (like 私に) is stated, the default assumption is the speaker (or the speaker’s in-group).

So:

先生は難しい文法を分かりやすい表現で説明してくれます。
→ By default: The teacher does this for me (or us, e.g., the class).

You can say:

先生は私に難しい文法を分かりやすい表現で説明してくれます。
= “The teacher explains difficult grammar to me in easy-to-understand terms.”

But often 私に is omitted because it’s obvious from context and from the use of くれる that the beneficiary is the speaker or their group.

Is 説明してくれます some kind of “present continuous” like “is explaining”? Why is there a て-form before くれます?

Here, the て-form is not marking progressive aspect (like “is doing”).
Instead, 説明して is the connecting form used with くれる to build the benefactive:

説明する → 説明して + くれる
= “explain + do (it for me)”
→ “explain for me.”

So:

説明してくれます is a single combined meaning:
“(He/She) explains (for me/us).”

Compare:

説明しています。
→ ている-form, progressive/habitual: “(He/She) is explaining / explains (generally).”
説明してくれます。
→ て + くれる benefactive: “(He/She) explains (for me/us).”

The て here works like a linker, not as part of the 〜ている aspect pattern.

Why is it くれます (non-past) and not くれました (past)? What exactly is the tense nuance here?

Japanese non-past (〜ます / dictionary form) covers both:

future actions, and
habitual / general actions.

In this sentence:

先生は難しい文法を分かりやすい表現で説明してくれます。
is most naturally understood as a habitual/generic statement:
“The teacher (always / generally) explains difficult grammar in easy-to-understand terms (for us).”

If you talk about a specific past event, you’d use past:

先生は難しい文法を分かりやすい表現で説明してくれました。
= “The teacher explained difficult grammar in easy-to-understand terms (for us).”

So:

くれます → regular / general behavior or future expectation.
くれました → one particular instance in the past.

Could I say 分かりやすく説明してくれます instead of 分かりやすい表現で説明してくれます? What’s the difference?

Yes, you can say:

先生は難しい文法を分かりやすく説明してくれます。

Here, 分かりやすく is the adverbial form of 分かりやすい, modifying the verb 説明する:

分かりやすく説明する = “to explain clearly / in an easy-to-understand way.”

Nuance difference:

分かりやすい表現で説明する
→ Focuses on the expressions/phrases used as the means:
“explain using easy-to-understand wording.”
分かりやすく説明する
→ Focuses more directly on the manner of explaining:
“explain in an easy-to-understand way / explain clearly.”

In everyday conversation, 分かりやすく説明してくれます is very common and natural.
The original sentence emphasizes that the specific 表現 (expressions, phrasing) themselves are easy to understand.

Can I change the word order, like putting 分かりやすい表現で earlier in the sentence?

Yes, Japanese word order is relatively flexible as long as elements stay before the main verb and particles stay with the words they mark.

These are all natural:

先生は難しい文法を分かりやすい表現で説明してくれます。
先生は分かりやすい表現で難しい文法を説明してくれます。

The basic structure is:

[Topic] は [Object] を [Means] で [Verb].

You can reorder 難しい文法を and 分かりやすい表現で without changing the core meaning much. The slight nuance:

If 難しい文法を comes closer to the verb, it may feel very slightly more focused on “difficult grammar” as what’s being explained.
If 分かりやすい表現で comes closer to the verb, it may slightly highlight “in easy-to-understand expressions” as the manner.

But in practice both 1 and 2 are very natural and mean the same thing to most listeners.

Why is 難しい just before 文法 with no particle, instead of something like 文法が難しい?

In Japanese, い-adjectives can directly modify nouns without any particle:

難しい文法 = “difficult grammar”
新しい本 = “new book”
高い山 = “tall mountain / high mountain”

This is like English “difficult grammar,” where “difficult” is directly before “grammar.”

On the other hand:

文法が難しいです。 = “Grammar is difficult.”
→ Here, 文法 is the subject and 難しい is the predicate.

So:

難しい文法を説明してくれます
→ “(He/She) explains difficult grammar (for me/us).”
→ “Difficult” is part of the noun phrase, not the sentence’s main predicate.

There’s no particle after 難しい because it’s not a separate clause; it’s just an adjective modifying a noun.