Learn Hardcore Japanese: senpai ha ii hito da ga, tokidoki isogasii. - My senior is a good person, but sometimes busy.

先輩 means a senior in your school, club, or workplace—someone who joined earlier or has more experience within the same group. You can address them as 田中先輩 or just 先輩 if the relationship is clear. It’s not a generic term for any older person; it’s role-based, not age-based.

Why is は used after 先輩 instead of が?

は marks the topic: 先輩は… means “as for senpai…,” then comments about them. が marks the grammatical subject and often introduces or emphasizes the subject. Here, setting 先輩 as the topic is natural because you’re describing them in general.

What does だ do after いい人?

だ is the copula (plain “is/are”) used after nouns and na-adjectives. いい人だ = “(someone) is a good person” in plain style. In polite style, use です: いい人です.

Why is there no だ after 忙しい?

忙しい is an i-adjective; i-adjectives don’t take だ. They already function as predicates: 忙しい = “is busy.” In polite speech you can say 忙しいです, but 忙しいだ is incorrect.

What does が mean here? Isn’t が also a subject marker?

Here が is the conjunction meaning but/however (as in …だが、…). It’s different from the subject-marking が. In this sentence, だが links two clauses in contrast.

Is だが formal? What are casual or polite alternatives?

だが is somewhat formal/bookish. Common alternatives:

Casual: だけど, けど
Neutral/polite: ですが, けれども Examples: 先輩はいい人だけど、ときどき忙しい。 / 先輩はいい人ですが、ときどき忙しいです。

Can I use でも instead of が?

Yes, but でも starts a new sentence. For example: 先輩はいい人だ。でも、ときどき忙しい。 This is conversational and natural.

Do I need the comma after が?

The 、 after が just marks a pause; it’s optional. …だが、ときどき… and …だがときどき… are both acceptable.

What does ときどき do, and where can it go?

ときどき is an adverb meaning “sometimes.” It can appear at the start or before the predicate: ときどき、先輩は忙しい。 / 先輩は、ときどき忙しい。 All are fine; position affects rhythm more than meaning.

Is ときどき the same as 時々?

Yes. ときどき (kana) and 時々 (kanji) are the same word. The 々 mark indicates repetition of the previous kanji (時→時). Both spellings are common.

Why are there spaces between the words in the example?

They’re for learner clarity. Standard Japanese writing doesn’t use spaces between words: 先輩はいい人だが、ときどき忙しい。

How do I pronounce the whole sentence? Why do I sometimes hear “sempai”?

Reading: せんぱいはいいひとだが、ときどきいそがしい。
Romaji: senpai wa ii hito da ga, tokidoki isogashii.
In casual speech, n + p often sounds like mp, so senpai can sound like sempai, but it’s still written senpai.

Is いい the same as 良い/よい? How do I negate or conjugate it?

Yes. The dictionary form is よい, but いい is more common in modern speech. Conjugations often use the よい base:

Negative: よくない (not いいくない)
Past: よかった (not いいかった) So: いい人 / よくない人 / いい人だった.

Why don’t we repeat “he/she” in the second clause?

Japanese uses topic continuity. Once 先輩 is set as the topic with は, it remains the understood subject for the following clause: …だが、（先輩は）ときどき忙しい。 No pronoun is needed.

Can I say 先輩はいい人だけど、ときどき忙しい? Do I need だ before けど?

Yes, that’s natural. With だけど/けど, you don’t add a separate だ after the noun phrase; だけど already contains the copula sense. So use いい人だけど, not いい人だけど.

How do I make a fully polite version without mixing styles?

Use です/ます consistently: 先輩はいい人ですが、ときどき忙しいです。 Avoid mixing plain だ with polite です in the same sentence unless you have a specific stylistic reason.

Could I say ときどきは忙しい? What’s the nuance?

ときどきは忙しい sets ときどき as a limited topic: “At those times, (they) are busy,” implying contrast with other times when they aren’t. ときどき忙しい is the neutral “(they are) sometimes busy.”

Does いい人 have any special nuance?

Literally it’s “a good person,” often “nice/kind.” Context decides whether it’s purely positive or the colloquial “nice (but maybe not exciting).” In this sentence it’s a straightforward compliment.