Learn Hardcore Japanese: watasi ha nihongo de mizikai meeru ga kakeru.

は marks the topic: what the sentence is “about”.
が marks the subject / thing that has the ability (especially with potential verbs like 書ける).

In 私は日本語で短いメールが書ける:

私は = “As for me / Speaking about me…”
短いメールが書ける = “(I) can write short emails.”

So the sentence structure is:

[Topic は] [Thing that can be done が] [Potential verb]
“As for me, short emails (I) can write (in Japanese).”

Using both is very common:

私は日本語が話せます。 – As for me, I can speak Japanese.
私は車が運転できます。 – As for me, I can drive a car.

What does で after 日本語 mean here?

で is the “means / method / in” particle.

日本語で literally means “by means of Japanese” → naturally translated as “in Japanese” (when talking about language).

Common patterns:

英語で話す – to speak in English
ペンで書く – to write with a pen
バスで行く – to go by bus

So in this sentence:

日本語で = “in Japanese (using Japanese as the medium)”
日本語で短いメールが書ける。 = “(I) can write short emails in Japanese.”

What kind of word is 短い, and why is it before メール?

短い is an i-adjective (形容詞 / い形容詞).

Its dictionary form ends in い: 短い (みじかい) – short.
As an adjective, it directly modifies a noun by coming before it.

So:

短いメール = “a short email / short emails”
長いメール = “a long email / long emails”
短い手紙 = “a short letter”

You must keep the い when it directly modifies a noun:

✔ 短いメール
✖ 短メール (wrong as a direct translation of “short mail”)

Why is the verb 書ける used instead of 書く?

書ける is the potential form of 書く.

書く – to write
書ける – can write / be able to write

So:

短いメールを書く – to write short emails (simple action)
短いメールが書ける – can write short emails (ability / possibility)

The sentence is about ability, not just the action, so Japanese uses the potential form:

私は日本語で短いメールが書ける。
“I can write short emails in Japanese.”

Why is there no です or だ at the end?

With verbs (including potential verbs like 書ける), you normally do not add だ or です after them.

The verb itself expresses the predication (what’s being said).
だ / です come after nouns or na-adjectives, not after plain verbs.

Examples:

学生だ / 学生です – “(I) am a student.” (noun)
静かだ / 静かです – “(It) is quiet.” (na-adjective)
書ける。 – “(I) can write.” (verb; complete as is)
書けます。 – polite verb form; still no です.

So:

✔ 私は日本語で短いメールが書ける。
✔ 私は日本語で短いメールが書けます。 (polite)
✖ 私は日本語で短いメールが書けるです。

Can I say メールを instead of メールが with 書ける?

With potential verbs (like 書ける, 読める, 食べられる), the thing that can be done is most commonly marked by が, not を.

So the standard pattern is:

Noun が書ける – can write Noun
Noun が読める – can read Noun
Noun が食べられる – can eat Noun

Thus:

短いメールが書ける。 – natural, standard
短いメールを書ける。 – possible in some modern speech, but sounds less natural and is not the “textbook-standard” pattern.

For learners, it’s best to strongly prefer が with potential verbs:

日本語が話せる。 – can speak Japanese
漢字が読める。 – can read kanji
短いメールが書ける。 – can write short emails

Is 私は necessary? Can I drop 私?

私 can be dropped if it’s clear from context who the subject is. Japanese frequently omits pronouns.

私は日本語で短いメールが書ける。
日本語で短いメールが書ける。 (no 私)

Both can be correct. The second one would usually still be understood as “I can write short emails in Japanese.” if the conversation is clearly about your abilities.

When do you include 私は?

When you want to contrast yourself with others:
- 私は日本語で短いメールが書けるけど、弟は書けない。
  “I can write short emails in Japanese, but my little brother can’t.”
When it’s not clear who you’re talking about yet.

Otherwise, especially in casual conversation, 私 is often omitted.

Why use は with 私 instead of が? What’s the difference?

は marks the topic, and が usually marks the subject (especially new or focused information).

私は日本語で短いメールが書ける。
“As for me, I can write short emails in Japanese.”
私が日本語で短いメールが書ける。
This is unusual; you generally don’t stack が like this.
More natural focus version would change structure, e.g.:
日本語で短いメールが書けるのは私だ。 – “The one who can write short emails in Japanese is me.”

In your sentence:

私は = topic: “speaking about me”
短いメールが書ける = comment about that topic

If you used 私が in a different structure, it would strongly emphasize “I (and not someone else)” as the one with the ability. But for a simple self-statement, 私は … が … is the normal pattern.

What is the politeness level of this sentence, and how do I make it polite?

書ける is the plain (dictionary) form, so the sentence is:

Casual / neutral style.

To make it polite, change the verb to ます form:

私は日本語で短いメールが書けます。

Differences:

書ける。 – plain; used with friends, family, in informal writing.
書けます。 – polite; used in most everyday conversations with non-intimates, in customer service, etc.

The rest of the sentence (私 / 日本語 / 短いメール) does not change; politeness is carried mainly by the verb form.

Can I change the word order? For example, where can I put 日本語で or 短いメール?

Japanese word order is fairly flexible before the verb, as long as particles are correct.

All of these are grammatical and natural:

私は日本語で短いメールが書ける。
私は短いメールが日本語で書ける。
日本語で私は短いメールが書ける。 (has a slight emphasis on “in Japanese”)

The most neutral, common order here is probably 1, with 日本語で relatively early.

You cannot move the verb away from the end:

✖ 私は書ける日本語で短いメール。 (wrong; verbs go at the end of the clause)

As long as で, が, は stay attached to the correct words, and the verb stays at the end, small word-order changes just add subtle emphasis differences, not big meaning changes.

What’s the difference between 書ける and 書くことができる?

Both can mean “can write”, but they differ in style and nuance:

書ける – potential verb
- Short, natural, commonly used in speech.
- Slightly more casual/neutral.
書くことができる – “to be able to write”
- More formal, heavy, often used in official writing, explanations, manuals, etc.
- Feels a bit longer and more “serious”.

Compare:

私は日本語で短いメールが書ける。
“I can write short emails in Japanese.” (normal, everyday)
私は日本語で短いメールを書くことができます。
“I am able to write short emails in Japanese.” (more formal/polite, e.g. on a resume or in a written self-introduction)

In most everyday situations, 書ける / 書けます is perfectly natural and preferred.

Why is メール used instead of 手紙? What nuance does メール have?

メール is a loanword from English “mail”, and in modern Japanese it usually means:

Email
Or short text-style messages (depending on context)

手紙 (てがみ) means (paper) letter.

So:

短いメールが書ける。 – “(I) can write short emails.” (modern, digital communication)
短い手紙が書ける。 – “(I) can write short letters.” (physical letters)

Using メール here suggests you’re talking about modern electronic messages, which matches how people commonly communicate today.