Learn Hardcore Japanese: kyou ha kibun ga ii desu kara, tosyokan de nihongo wo benkyousimasu. - Because I feel good today, I will study Japanese at the library.

は is the topic marker. 今日は means “as for today” or “today (speaking about today).” It frames the rest of the sentence as information about today. Note the particle は is pronounced “wa” here. Without は, 今日 can function as a simple time adverb; with は, it adds a slight contrast or emphasis on “today.”

Why does 気分 take が (気分がいい) and not は?

With descriptive predicates (like adjectives), が marks the thing that has the property. 気分がいい states a neutral fact: “(my) mood/condition is good.” Using 気分はいい is possible but tends to contrast it with something else (e.g., “the mood is good, but…”). So が is the default in plain descriptions.

What’s the difference between 気分, 気持ち, and 調子?

気分: mood/overall feeling (often physical/mental condition). Common with いい/悪い. Example: 今日は気分がいい.
気持ち: feeling/sensation; often about how something feels. Example: このお風呂は気持ちがいい (This bath feels good).
調子: condition/performance of a body part, one’s performance, or a machine. Example: 体の調子がいい (My body’s condition is good).

Why is it いい and not よい? Are they the same?

They’re the same adjective. よい is the original/formal form; いい is the common colloquial form. Conjugations often use よ: よく (adverb/te-form), よかった (past), よくない (negative). So you say いいです but よくない, よかった.

Do I need です before から? Is 今日は気分がいいから also correct?

Both are correct:

今日は気分がいいですから… (fully polite style)
今日は気分がいいから… (less formal, very common in speech) With i-adjectives like いい, adding です keeps a consistent polite tone. In casual speech, people often drop it.

What’s the difference between から and ので here?

Both mean “because,” but:

から is more direct and is commonly used with intentions, suggestions, or commands.
ので sounds softer/more objective. With na-adjectives/nouns you use な before ので (静かなので). Polite style allows ですので. In this sentence, either works: 今日は気分がいいので、… is just a bit softer.

Can I put the reason at the end instead?

Yes, though reason-first is more common. Two natural options:

今日は気分がいいから、図書館で日本語を勉強します。
図書館で日本語を勉強します。今日は気分がいいから。 The second is conversational and adds the reason after the statement.

Why 図書館で and not 図書館に?

で marks the location where an action occurs: 図書館で勉強します (study at the library).
に marks destination/time/existence: 図書館に行きます (go to the library), 図書館にいます (be at the library).

Why 日本語を and not 日本語が?

を marks the direct object of an action verb. 日本語を勉強します = “study Japanese.” Using が would make 日本語 the subject (e.g., 日本語が分かります “I understand Japanese,” where Japanese is the thing understood).

Do I need to say “I”? Why is the subject omitted?

Japanese often omits pronouns when context makes them clear. Here, it’s naturally understood that the speaker is talking about themselves: “(I) feel good today, so (I) will study…”

Does 勉強します mean “will study” or “study”?

Non-past polite (〜ます) can mean habitual present or future. With 今日は, it implies a plan/intention for today (“will study today”). To emphasize intention/schedule:

勉強するつもりです (I intend to study)
勉強する予定です (I’m scheduled/planning to study)
勉強しようと思います (I’m thinking of studying)

Can I change the word order to 日本語を図書館で勉強します?

Yes. Both 図書館で日本語を勉強します and 日本語を図書館で勉強します are natural. Japanese allows some flexibility; everything modifies what comes before the verb.

In casual speech, can I drop particles and be more brief?

Yes, in casual conversation people often drop です/ます and sometimes particles:

今日は気分いいから、図書館で日本語勉強する。 Keep particles in formal speech/writing, and be careful not to drop particles that would cause ambiguity.

Is the comma before 図書館 necessary?

No, but it helps readability. You can write it with or without a comma: …ですから図書館で… or …ですから、図書館で…. Japanese punctuation is flexible.

Do Japanese normally write with spaces like this?

No. Spaces were added for learners. Normally you’d write: 今日は気分がいいですから、図書館で日本語を勉強します。

What’s the difference between です and ます in this sentence?

です is the polite copula used with nouns/na-adjectives and appended to i-adjectives for politeness: いいです.
ます is the polite verb ending: 勉強します. Using both keeps the whole sentence in polite style.

Can I say 日本語の勉強をします instead of 日本語を勉強します?

Yes:

日本語を勉強します (verb takes a direct object) — straightforward and common.
日本語の勉強をします (“do study of Japanese”) — slightly more formal/explanatory in tone.
勉強をします alone is also acceptable (“I’ll study”), but less specific.

Can I use the て-form to give the reason, like 気分がよくて…?

Sometimes, but be careful. The て-form can link cause-effect for factual/resulting situations, e.g., 気分がよくて、たくさん歩いた. However, using て to justify a volitional act or command can sound off. For clear “because, so I will/let’s/please” relationships, prefer から/ので.

When do I use だから vs ですから vs から?

After a noun/na-adjective (plain): 学生だから (because [I] am a student), 静かだから.
Polite linking: 学生ですから／静かですから／便利ですから.
After a verb or i-adjective (plain): 行くから, 寒いから, 気分がいいから. (i-adjectives don’t take だ.) Also, ですから at the start of a sentence can mean “therefore” referring to the previous sentence.

How else can I say “I feel good today”?

今日は気分がいいです。 (neutral, very common)
今日はいい気分です。 (more “I’m in a good mood”)
今日は体調がいいです。 (my physical condition is good) All are natural; choose based on nuance.