Learn Hardcore Japanese: watasi ha yoru ni tegami wo kakimasu ga, asa ha kakimasen. - I write letters at night, but I do not write them in the morning.

In time expressions, に marks a specific point or period when something happens. Here, 夜に means “at night.” Without に, 夜 would be more like a general topic (“as for night”), but with に it pinpoints the time you write.

Why is 朝 marked with は instead of に in the second clause?

Using 朝は sets up a contrast with 夜に. It’s saying “As for the morning (in contrast to the night), I don’t write.” If you said 朝に書きません, you’d simply state “I don’t write in the morning,” but 朝は書きません emphasizes “morning” as a contrasting topic.

What’s the role of the first は in 私は and how is it different from the は in 朝は?

Both are the topic marker は, but they focus on different things. 私は introduces “I” as the topic (“As for me…”). 朝は shifts the topic to “morning” to contrast with the previous time frame. Japanese often shifts the topic mid-sentence to highlight contrast or change focus.

What is the が after 書きます doing? Isn’t が the subject marker?

In this context, が is not the subject marker. It’s a conjunction meaning “but.” It connects two clauses: “I write letters at night” and “I don’t write in the morning.”

Why is 書きます used instead of the dictionary form 書く?

書きます is the polite present form of 書く. A learner might choose 書く for casual speech, but in many contexts Japanese speakers use ～ます to be polite or neutral.

How do you get the negative 書きません from 書きます?

To form the negative polite, you replace ～ます with ～ません. So 書きます → drop ます → 書き → add ません → 書きません (“do not write”).

Why does 手紙 come before 書きます in the sentence?

Japanese follows a Subject–Object–Verb order. 手紙を is the object marked by を, and it naturally precedes the verb 書きます (“write letters”).

Is it necessary to include 私は, or can you omit it?

You can usually omit 私は if context makes the subject clear. In Japanese, subjects/topics are dropped when obvious, so “(I) write letters at night, but (I) don’t write in the morning” is perfectly fine without 私は.

Could you switch and say 夜は手紙を書きます instead of 夜に手紙を書きます?

Yes, you could. 夜は手紙を書きます means “As for the night, I write letters,” making “night” the topic. The nuance shifts from indicating “at night” (specific time) to “the night” as a general setting or habitual topic.

What overall nuance does this sentence convey beyond a simple schedule?

By using 夜に and then contrasting 朝は, it highlights a clear habit or preference: you consistently write letters at night and, by contrast, never do so in the morning. The structure underscores that difference in your routine.