Learn Hardcore Japanese: genin ga wakaranai baai ha, senpai ni soudansiyou. - If you don't know the cause, let's consult a senior.

With 分かる, the thing that is understood (or not understood) is normally marked by が: Xが分かる = “understand/know X.” So 原因が分からない means “(I/you/we) don’t know the cause.” Using は inside this clause would shift to a contrastive topic: 原因は分からない (“As for the cause, [at least] we don’t know it”), which is possible but adds a contrastive nuance. The neutral, standard choice here is が.

Why can’t it be 原因を分からない?

Standard Japanese uses が with 分かる: Xが分かる. You will hear Xを分かる in some casual speech or dialects, but it’s nonstandard and best avoided in writing and in exams. Stick with 原因が分からない.

What’s the difference between 分かる and 知る?

分かる = to understand/recognize/realize; the understood thing takes が: 原因が分からない.
知る = to come to know (moment of learning). For ongoing knowledge, Japanese uses 知っている. To say “I don’t know the cause,” you can say 原因を知らない. Both 原因が分からない and 原因を知らない are fine; 分からない leans toward “can’t figure it out/understand,” while 知らない is “don’t have the information.”

Who is the subject in 原因が分からない? Isn’t it “I”?

Japanese often omits the “knower.” In 原因が分からない, the grammatical subject is actually the cause (the thing not understood). The person who doesn’t understand is implicit. You can make it explicit with 私は/僕は or 私には:

私は原因が分からない。
私には原因が分からない。 (adds “for me” nuance)

What does 場合 mean here, and how does the clause attach to it?

場合 (ばあい) means “case/situation.” The clause 原因が分からない directly modifies it, yielding “the case where the cause is not known.” So 原因が分からない場合 = “in the case that you don’t know the cause.” This is a common rule-like pattern in manuals and guidelines.

Why is there a は after 場合? Could it be 場合には?

は marks the conditional phrase as the topic: “As for the case where you don’t know the cause, …” Adding に gives 場合には, which is also common and can sound a bit more formal or emphatic. All of these are acceptable:

原因が分からない場合は、…
原因が分からない場合には、…

How is 場合 different from とき or なら?

～場合(は): formal, rule-like, covers hypothetical or general conditions.
～とき(は): “when,” more temporal and slightly less formal.
～なら: conditional “if,” often conversational and focuses on the given condition. All three can work, with nuance differences:
原因が分からないときは… (when you don’t know)
原因が分からないなら… (if you don’t know)

What does 相談しよう mean exactly?

相談しよう is the plain volitional form of 相談する, meaning “Let’s consult/discuss (ask for advice).” It’s an inclusive suggestion (speaker + listener). The polite equivalent is 相談しましょう. If you want a softer “let’s try,” use 相談してみよう/相談してみましょう.

What level of politeness is this sentence? How could I make it more polite?

As written (相談しよう), it’s a casual suggestion among peers. More polite options:

原因が分からない場合は、先輩に相談しましょう。
Instruction/request style: …先輩に相談してください。
With honorific noun: …先輩にご相談ください。 If you’re humbly stating what you will do, use …先輩にご相談いたします。

Why is it 先輩に and not 先輩と?

With 相談する meaning “to consult (someone for advice),” the person you consult takes に: Xに相談する. If you emphasize discussing with someone as a partner, と can appear (e.g., 家族と相談する = “discuss with family”), but when you seek advice from a senior, 先輩に相談する is the most natural. To name the topic, add について: 原因について先輩に相談する.

What’s the difference between 相談する and 聞く/尋ねる?

相談する: to consult/discuss a problem and seek advice (two-way discussion).
聞く/尋ねる: to ask (a question) or inquire. If you merely want a fact, use 聞く/尋ねる. If you need guidance or to talk through an issue, use 相談する. Also useful: 相談に乗る = “to give someone advice/help them by listening.”

What exactly does 先輩 mean? Is it about age?

先輩 (せんぱい) is a “senior” in experience or entry order (school, company, club), not necessarily older in age. You can address someone as 先輩 directly, or use a name + 先輩 (e.g., 田中先輩). Don’t say 先輩さん. In companies, people often use surname + さん instead; 先輩 here functions as a role label (“a senior colleague”).

Why 原因 and not 理由?

原因 = cause of a phenomenon or problem (mechanical failure, bug, illness).
理由 = reason/motive, often tied to a person’s decision or explanation. In troubleshooting contexts, 原因 is the natural choice: “the cause.”

How do I pronounce 場合? And the other words?

場合: ばあい (ba-ai; two vowel beats, not “bai”).
原因: げんいん.
分からない: わからない.
先輩: せんぱい (the ん before p sounds like “m” in fast speech, but it’s written ん).
相談しよう: そうだんしよう (shi-you; not “しょう” by itself).

Are spaces normal in Japanese writing?

No. Spaces were added here for learners. In ordinary Japanese, the sentence appears as 原因が分からない場合は、先輩に相談しよう。

Can I say 先輩に相談してみよう instead?

Yes. ～てみる adds a “give it a try” nuance: 先輩に相談してみよう = “Let’s try consulting a senior.” It can feel a bit softer or exploratory.

Is 原因が知らない acceptable?

No. With 知る/知らない, the thing known takes を and the knower is the subject: 私は原因を知らない (“I don’t know the cause”). Saying 原因が知らない is ungrammatical because it makes the cause the subject that “doesn’t know.” If you want the cause as the grammatical subject, use 分かる: 原因が分からない.

Could I use なら or たら instead of 場合は?

Yes, with small nuance shifts:

原因が分からないなら、先輩に相談しよう。 (if it’s the case that…)
原因が分からなかったら、先輩に相談しよう。 (if you end up not knowing/if it turns out you don’t know) 場合は sounds more rule-like and formal, common in written guidance.