sensei wa muzukashii bunpou o wakariyasui hyougen de setsumeishite kuremasu.

The teacher explains difficult grammar using easy-to-understand expressions.

Breakdown of sensei wa muzukashii bunpou o wakariyasui hyougen de setsumeishite kuremasu.

• は: topic particle
• を: direct object particle
• 先せん生せい: teacher
• で: means particle

Questions & Answers about sensei wa muzukashii bunpou o wakariyasui hyougen de setsumeishite kuremasu.

What is the role of は in 先生は? Why not 先生が?

は marks the topic of the sentence, not necessarily the grammatical subject.

• 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 mean, and how is it formed?