Learn Hardcore Japanese: watasi ha natuyasumi ni nihongo wo takusan benkyousuru tumori desu. - I plan to study a lot of Japanese during summer vacation.

つもりです expresses a personal intention or resolve: “I intend to.” 勉強します (non‑past polite) can also refer to the future, but it’s a more neutral statement of what will happen; it doesn’t highlight your inner decision as much. 予定です is “it’s scheduled/planned”; it sounds more fixed, like something on a calendar. So, from most “inner intention” to most “externally set plan”: つもり → (plain non‑past) → 予定.

Why is it 勉強するつもりです and not 勉強しますつもりです?

Before つもり, the verb must be in plain (dictionary) form, not ます form. So it’s V‑dictionary + つもり: 勉強するつもりです. For a negative intention, use the plain negative: 勉強しないつもりです (“I intend not to study”).

Why is there です at the end?

つもり is a noun (“intention”), so the sentence ends with the copula: つもりだ/です. Polite style uses です: 勉強するつもりです. Plain style is 勉強するつもりだ.

Can I drop 私（は）?

Yes. Japanese often omits obvious subjects. 夏休みに日本語をたくさん勉強するつもりです is perfectly natural. Keep 私は when you need contrast or emphasis (e.g., “As for me…”).

Why is it 夏休みに and not 夏休みで? Can I say 夏休みは/には?

に marks a time point/period when something happens (“in/at/on”). で doesn’t mark time like that, so 夏休みで is not used here. You can topicalize: 夏休みは日本語を… (“As for summer vacation, I will…”), or emphasize the time by keeping both: 夏休みには日本語を…. 夏休みには often adds a “when it’s summer break (as opposed to other times)” nuance.

Where should たくさん go? Is たくさんの日本語 okay?

Most natural here is 日本語をたくさん勉強する. たくさん日本語を勉強する is also fine. Don’t say たくさんの日本語を勉強する to mean “study a lot of Japanese (in general)”; that sounds like “many Japanese [items]” and is odd unless you mean many words/texts. Let たくさん modify the action, not the language.

Can I use よく or いっぱい instead of たくさん?

たくさん = “a lot/much” (quantity/amount of studying).
よく = “often” or “well” (“study often” or “study well/hard,” depending on context).
いっぱい = “a lot,” but casual/colloquial.
So pick たくさん for “a lot (in quantity/time),” よく for “often/well,” and いっぱい for casual speech.

Is the object marker を required after 日本語?

Yes, in standard Japanese the direct object takes を: 日本語を…. In casual speech people sometimes drop particles, but as a learner you should keep を, especially in writing or polite style.

Where’s the future tense? Why is everything in “present” form?

Japanese has no dedicated future tense. The non‑past form covers present and future. Future meaning comes from context or expressions like つもり, 予定, or time words (e.g., 明日).

What’s the difference between 勉強する, 習う, and 学ぶ?

勉強する: to study (general/self‑study or coursework).
習う: to learn from someone; typically takes a teacher with に (e.g., 先生に日本語を習う).
学ぶ: to learn/study in a more formal or academic sense.
In this sentence, 勉強する is the most natural.

Is 日本語の勉強をたくさんするつもりです also natural?

Yes. 勉強する and 勉強をする are both common. Using the noun phrase version gives 日本語の勉強をたくさんするつもりです (“I intend to do a lot of Japanese study”).

How do I say I don’t intend to, or speak about past intention?

Negative intention: 日本語をたくさん勉強しないつもりです or more emphatically 日本語をたくさん勉強するつもりはありません.
Past intention: 日本語をたくさん勉強するつもりでした (“I intended to study a lot”).
Note also V‑た + つもりだ means “I believe/consider I did V,” which is a different pattern (e.g., 勉強したつもりだ = “I thought I studied”).

Can I use 夏休み中に or 夏休みの間に instead of 夏休みに?

Yes. 夏休み中(に) emphasizes “during/throughout summer vacation.” 夏休みの間(に) means “during the period of summer vacation (at some point or throughout).” All are fine; pick based on whether you want to stress “during that period.”

Can I use つもり for someone else’s plans?

You can if you’re confident about their intention: 彼は日本語をたくさん勉強するつもりです. But since つもり refers to someone’s inner state, it’s common to add a source: …つもりだと言っています／だそうです. If it’s a fixed plan, …する予定です is safer and less presumptive.