In short

The volitional (意向形 ikōkei) is the plain-form twin of the ましょう you already use: 行きましょう -> 行こう ikō (“let’s go”). On its own it is a casual “let’s” or a pep talk to yourself; stacked with と思います it states your intention. For a plan you have decided on, use V-plain + つもりです; for something on a schedule, V-plain + 予定です.

The rule

Step 1 - Build the form. The volitional is one syllable of change on the dictionary form, and the three verb classes behave exactly as they do everywhere else.

• 五段 (Group I): move the last kana to the お-row and add う (く -> こ + う), which always sounds as a long -ō. 行く iku -> 行こう ikō, 飲む nomu -> 飲もう nomō, 待つ matsu -> 待とう matō, 買う kau -> 買おう kaō. Work from the kana, not from the romaji: つ moves to と (matsu -> matō, not “matsō”) and う moves to お (kau -> kaō).
• 一段 (Group II): drop る and add よう. 食べる taberu -> 食べよう tabeyō, 見る miru -> 見よう miyō.
• Irregular: する -> しよう shiyō; 来る -> 来よう koyō (the reading shifts to ko-, as in 来ない konai).

There is no everyday negative volitional: the negative counterpart 〜まい (行くまい) is literary and survives mainly in the set pattern under “Looking ahead” below. In ordinary speech “let’s not” is said with a different verb: 行くのはやめましょう iku no wa yamemashō (“let’s drop going”).

Step 2 - Use it bare, in plain style. By itself the volitional is casual, so it belongs with friends and family, or with yourself:

• Casual invitation - そろそろ帰ろう。 Sorosoro kaerō. (“Let’s head back.”) The polite version is ましょう; never mix the two in one sentence.
• Self-talk and self-encouragement - 頑張ろう。 Ganbarō. (“Let’s do this / I’ll give it my best.”) もう寝よう。 Mō neyō. (“Right, bed.”)
• Casual “shall we?” - add か: 何を食べようか。 Nani o tabeyō ka. This is the plain counterpart of 〜ましょうか from Expressing desire, invitations and offers, which stays the polite choice for offering help (手伝いましょうか Tetsudaimashō ka, “Shall I help?”).

Step 3 - 〜(よ)うと思います: your intention. Put the volitional inside the quotation particle と (Quotation と／という／って) and follow with 思います. The sentence can be polite at the end while the quoted verb is plain - this is the register rule of the whole A2 band: subordinate clauses take plain forms.

V-volitional + と思います = “I think I’ll …” - a decision you are making as you speak.

Do not confuse it with V-plain + と思います, which is a guess about a fact:

• 行こうと思います Ikō to omoimasu - “I think I’ll go.” (my intention)
• 行くと思います Iku to omoimasu - “I think he’ll go.” (my prediction)

Step 4 - 思います vs 思っています. Switching 思う to the 〜ている form (〜ている) turns the moment into a state:

• 〜(よ)うと思います - decided just now, announced on the spot.
• 〜(よ)うと思っています - a standing intention you have been holding for a while. Common with 前から mae kara (“for some time now”).

There is also a grammatical restriction: plain 思います can only report the speaker’s own mind, because you cannot look inside someone else’s head. For a third person you must use 思っています (or add hearsay). So ×彼は留学しようと思います is wrong; say 彼は留学しようと思っています Kare wa ryūgaku shiyō to omotte imasu (“he is thinking of studying abroad”). A question is the one exception, because it asks the listener about the listener’s own mind: 留学しようと思いますか Ryūgaku shiyō to omoimasu ka is fine.

Step 5 - 〜つもりです: a settled personal plan. つもり is a noun (“intention”), so it takes a noun-modifying clause in front of it (Relative clauses) - the dictionary form, never the volitional. It is firmer and more considered than 〜と思っています.

• Positive: V-plain (dictionary) + つもりです - 買うつもりです kau tsumori desu.
• Negative, two strengths:
  • V-ない + つもりです - “I intend not to”: 買わないつもりです kawanai tsumori desu. A decision with a negative content.
  • V-plain + つもりはありません - “I have no intention of”: 買うつもりはありません kau tsumori wa arimasen. This denies the intention itself and is much blunter - close to refusing.

つもり can be contradicted by reality. With the た-form it means “I was under the impression that I had”: 説明したつもりです setsumei shita tsumori desu (“I thought I’d explained it” - apparently not). Likewise 若いつもりです wakai tsumori desu (“I like to think I’m still young”). This flavour is why つもり can sound presumptuous about other people - use 予定 when asking about someone else’s arrangements.

Step 6 - 〜予定です: what the calendar says. 予定 yotei (“schedule”) is also a noun and also takes the dictionary form, but it reports a plan fixed by arrangement rather than by your will. It works with events, not just people: 会議は三時から始まる予定です Kaigi wa san-ji kara hajimaru yotei desu. With a noun, insert の: 出発は明日の予定です Shuppatsu wa ashita no yotei desu.

Step 7 - 〜(よ)うとする: trying, or on the verge. The volitional + とする has two readings, both very frequent:

• An attempt - 開けようとしましたが、開きませんでした akeyō to shimashita ga, akimasen deshita (“I tried to open it, but it wouldn’t open”). Note that 〜てみる from te-form auxiliaries means “try and see how it goes”; 〜(よ)うとする means “make the effort”, typically when it fails.
• On the verge - with 〜としたとき or 〜としています: 出ようとしたとき deyō to shita toki (“just as I was about to leave”). Here the subject need not even be a person: 電車が出ようとしています Densha ga deyō to shite imasu (“the train is about to leave”).
• Negative 〜(よ)うとしません = “refuses to, won’t”: 子どもが薬を飲もうとしません Kodomo ga kusuri o nomō to shimasen (“the child won’t take the medicine”).

Looking ahead. The volitional also feeds a formal concession pattern, 〜(よ)うが〜まいが／〜(よ)うと〜まいと (“whether or not …” - が pairs with が, と with と), as in 行こうが行くまいが ikō ga ikumai ga (“whether one goes or not”); まい attaches to the dictionary form of a 五段 verb. That is C1 material and waits for Universal concession and literary contrast.

Forms & patterns

The volitional paradigm. Compare the polite ましょう column you already know.

What each intention pattern attaches to. Getting the form in front of the pattern right is most of the battle.

つもり vs 予定.

Examples

Common mistakes

• 行きましょうと思います。 (Ikimashō to omoimasu.) -> 行こうと思います。 (Ikō to omoimasu.) - The clause before と is subordinate, so it must be plain. ましょう is a polite sentence ending and cannot be quoted; the politeness lives on 思います at the end.
• きようと思います。 (Kiyō to omoimasu.) -> 来ようと思います。 (Koyō to omoimasu.) - 来る is irregular. Its volitional keeps the ko- reading, like 来ない konai and 来られる korareru - not the ki- of 来ます.
• 日本へ行こうつもりです。 (Nihon e ikō tsumori desu.) -> 日本へ行くつもりです。 (Nihon e iku tsumori desu.) - つもり is a noun, so it is modified by the dictionary form. The volitional attaches to と (と思う, とする) but never modifies a noun, so it cannot stand before つもり or 予定.
• 彼は会社をやめようと思います。 (Kare wa kaisha o yameyō to omoimasu.) -> 彼は会社をやめようと思っています。 (Kare wa kaisha o yameyō to omotte imasu.) - Plain 思います reports only your own mind. Another person’s intention is a state you observe, so it takes 思っている.
• 電車は九時に出るつもりです。 (Densha wa ku-ji ni deru tsumori desu.) -> 電車は九時に出る予定です。 (Densha wa ku-ji ni deru yotei desu.) - つもり needs a subject that can intend things. Trains, meetings and flights have 予定, not つもり.

Tips

• One test decides つもり or 予定: who fixed it? If it is your decision and could still change, use つもり. If a timetable, a booking or your boss fixed it, use 予定. Learners who default to つもり end up claiming to have talked the airline into its departure time.
• The 五段 volitional is the ない-form’s kana moved from the あ-row to the お-row. If you know 行かない, you know the slot: 行か -> 行こ, 飲ま -> 飲も, 待た -> 待と. The exception is verbs ending in う, whose ない-form takes わ but whose volitional still takes お: 買わない but 買おう. Every 五段 verb lands on the お-row plus う, so the sound is always a long -ō: nomō, matō, kaerō. Writing it as “nomou” or shortening it to “nomo” is the commonest romaji slip.
• と思います is not always modest. Because 〜(よ)うと思います states a decision rather than softening it, it is the normal way to announce plans at work - 明日、確認しようと思います Ashita, kakunin shiyō to omoimasu (“I’ll check tomorrow”) sounds organised, not hesitant. To sound tentative instead, reach for 〜たいと思っています or a conjecture form from Conjecture でしょう／だろう and かもしれない.
• 〜(よ)うとした usually means it did not happen. 開けようとしました akeyō to shimashita implies the thing stayed shut, and 出ようとしたとき means you never got out of the door. If the attempt actually succeeded, drop the pattern and just use the plain past: 開けました akemashita.