する-Compound Verbs (勉強する・電話する)

Once you know the irregular verb する ("to do"), you get an enormous bonus for free: noun + する turns a huge class of nouns into verbs. 勉強 ("study") + する = 勉強する ("to study"); 電話 ("telephone") + する = 電話する ("to phone"); 予約 ("reservation") + する = 予約する ("to reserve"). This single pattern generates thousands of verbs, absorbs almost any new loanword, and — best of all — asks you to conjugate only one thing: する. The noun never moves.

Why this pattern exists: many English verbs are Japanese nouns

Here is the reframe that makes the whole system click. A great many concepts that English packages as a verb ("to study," "to phone," "to reserve," "to marry," "to drive") are packaged in Japanese as a noun — 勉強, 電話, 予約, 結婚, 運転 — plus the light verb する to activate it. So instead of learning a brand-new verb, you learn a noun and let する do all the grammatical work. The noun carries the meaning; する carries the tense, politeness, and negation.

Only する conjugates — the noun is frozen

This is the labor-saving heart of the pattern: whatever the tense, politeness, or polarity, only する changes. The noun 勉強 sits there untouched while する runs through its irregular paradigm. Learn する once (its full page is the irregular verb する) and you can inflect every する-noun in the language.

Notice the potential is 勉強できる (dekiru), not ×勉強しられる — because する's potential is the suppletive できる. That, too, transfers to every する-noun automatically.

The を split: 勉強する ≈ 勉強をする — but idiom by idiom

Because the first half really is a noun, it can often take the object particle を and detach: 勉強をする means essentially the same as 勉強する ("do studying" ≈ "study"). The を version tends to feel slightly more concrete or deliberate ("do some studying"), while the fused version is the neutral default.

But — and this is the honest, un-shortcut-able part — whether a given noun splits comfortably with を is a per-word idiom, not a rule you can predict. 電話する ↔ 電話をする are both perfectly natural. 勉強する ↔ 勉強をする, both fine. Yet 結婚する ("marry") almost never becomes ×結婚をする in normal speech, and 心配する ("worry") resists 心配をする. There is no clean logic here; you simply learn, per noun, whether the split sounds native. The safe habit: treat する-nouns as vocabulary, default to the fused form (noun + する), and only split with を for the words where you've actually heard it.

The double-を trap

There is one place where the を split creates a real grammatical clash. If the noun already has its own object marked with を, you cannot also detach the する-noun with を — Japanese does not tolerate two を objects in one clause. So 日本語を勉強する is fine, but you must not "improve" it to ×日本語を勉強をする.

If you want the を-split and an object, restructure with の: 日本語の勉強をする ("do the studying of Japanese") is grammatical, because now 日本語 modifies 勉強 with の and only one を remains.

Loanwords join instantly

The pattern is so productive that almost any imported noun becomes a verb the moment you add する. This is how Japanese verbs new technology and borrowed actions on the fly: コピーする ("copy"), キャンセルする ("cancel"), チェックする ("check"), ダウンロードする ("download"), クリックする ("click"). No new conjugation to learn — する handles all of it.

How this differs from English

English has light-verb constructions too — "make a phone call," "do the cleaning," "give an explanation" — but they are the marked, wordy option; the default is a plain verb ("phone," "clean," "explain"). Japanese inverts that priority: for this whole class of concepts, the noun + する construction is the ordinary verb, and there is often no single-word alternative at all. So the mental shift for an English speaker is to stop looking for a dedicated verb and instead ask, "what noun names this action, and does する turn it on?" Nine times out of ten, it does.

Common Mistakes

1. Trying to conjugate the noun. The noun is frozen. You never inflect 勉強 itself — する carries every change.

2. Assuming every noun splits with を. Many don't. 結婚する rarely becomes 結婚をする.

3. Using しられる for the potential. する's potential is the suppletive できる, so it's 運転できる, not ×運転しられる.

4. Stacking two を. An object already marked with を blocks a second を on the する-noun.

Key Takeaways

• Noun + する verbs a noun — 勉強する, 電話する, 予約する, 結婚する, 運転する — and covers thousands of verbs, including every new loanword (コピーする, キャンセルする).
• Only する conjugates. The noun is frozen; learn する's paradigm once and you inflect them all (note the potential is できる, e.g. 運転できる).
• The を split (勉強 → 勉強をする) works for some nouns and not others — it's a per-word idiom, so default to the fused form and split only where you've heard it.
• Never stack two を: 日本語を勉強する (fused), not ×日本語を勉強をする. Use の if you need both (日本語の勉強をする).