Learn Hardcore Japanese: tugi no siken no tame ni, sakusen wo kimemasyou. - Let's decide on a strategy for the next exam.

The particle の in 次の試験 is the genitive (or attributive) particle. It links two nouns so that the first noun, 次 (next), modifies the second noun, 試験 (exam), giving the meaning “the next exam.” You wouldn’t use が or を here because you’re not marking a subject or object—you’re simply forming a noun‐to‐noun modifier.

How can I tell that 次の modifies 試験 and not 作戦?

In Japanese, modifiers (including a noun+の phrase) always come immediately before the noun they modify. Here, 次の is directly before 試験, so it attaches to 試験. The later word 作戦 is too far away to be modified by 次の, and there’s no particle or connector linking them. Word order and proximity are your cues.

What does ために mean in 試験のために, and why do we say 試験のために instead of just 試験のため?

ため is a noun meaning “sake” or “benefit,” and when you add に you get ために, which marks purpose: “for the purpose of…”
– 試験のために literally means “for the sake of the exam” → “for the next exam.”
Without に, 試験のため can stand alone as a noun phrase, but it won’t function adverbially to express purpose. The に turns the phrase into an adverbial clause indicating why you’re doing something.

Is the comma 、 after ために mandatory? Can it be omitted?

Japanese commas (読点) are mainly for readability. The comma after ために introduces a slight pause before the main clause 作戦を決めましょう. It isn’t strictly mandatory—especially in very short or informal sentences you might skip it—but in most written Japanese it’s included to help the reader parse the purpose clause from the main action.

What’s the nuance difference between 作戦 and 計画? Could I use 計画 here instead?

– 作戦 (さくせん) carries the sense of a “strategy” or “tactic,” often implying a deliberate, action‐oriented approach (think military or game strategies).
– 計画 (けいかく) is a more general “plan” or “scheme,” focusing on scheduling or organizing steps.
You could say 計画を決めましょう (“Let’s decide a plan”), but using 作戦 emphasizes that you want a strategic, perhaps tactical, approach for tackling the exam.

What is the function of を in 作戦を決めましょう?

The particle を marks 作戦 as the direct object of the verb 決める (“to decide”). In other words, 作戦 is what you’re deciding. Without を, the verb wouldn’t know what its object is.

Why is the verb in the volitional form 決めましょう, and how is it different from 決めます or 決めよう?

決めましょう is the polite volitional or “let’s” form of 決める, used to make a suggestion—“let’s decide.”
– 決めます is plain polite: “I/we will decide” or “we decide,” a statement rather than a suggestion.
– 決めよう is the plain volitional: “let’s decide,” used in casual speech among friends.
So 決めましょう strikes a balance: it’s inviting (“let’s do this together”) while remaining polite.

Could I reorder the sentence to 作戦を次の試験のために決めましょう? Would it still make sense?

Yes. Japanese word order is flexible because particles mark grammatical roles.
– 作戦を次の試験のために決めましょう still means “Let’s decide a strategy for the next exam.”
Shifting 次の試験のために after 作戦を may slightly shift your emphasis—from highlighting the exam’s purpose first to focusing on “the strategy” itself—but the core meaning remains intact.