densha wa hayakute benri desu.

Trains are fast and convenient.

Breakdown of densha wa hayakute benri desu.

• は: topic particle
• です: to be
• 電車でんしゃ: train
• 便利べんり: convenient
• 速はやい: fast
• 〜くて: connective form

Questions & Answers about densha wa hayakute benri desu.

What does the particle は do in 電車は速くて便利です?

は marks 電車 as the topic of the sentence—what you’re talking about. It doesn’t necessarily mark the subject (the doer) but shows that we’re commenting on “trains,” namely that they are fast and convenient.

Why is 速い changed to 速くて when connecting to 便利?

In Japanese, to link an i-adjective to another predicate (another adjective or verb), you turn the i-adjective into its て-form:

1. Drop い from 速い → 速
2. Add くて → 速くて
   This て-form connection means “and,” so 速くて便利です = “is fast and (therefore) convenient.”

Why can’t we say 電車は速くです?

Because for predicates, an i-adjective uses its dictionary form plus です:
• Correct: 電車は速いです
The form 速くです would be the adverbial form plus です, which is ungrammatical in Japanese.

What kinds of adjectives are 速い and 便利, and how do they behave differently?

• 速い is an i-adjective (ends in い). Its て-form is 速くて. For a predicate you say 速いです or 速いだ (plain).
• 便利 is a na-adjective. When modifying a noun, you need 便利な本, but as a predicate you simply attach the copula: 便利です (or plain 便利だ).

Why don’t we say 便利なです or 便利な before です?

When a na-adjective stands alone as a predicate, you drop な and add the copula: 便利です. The な only appears when the na-adjective directly modifies a noun (e.g. 便利な道).

What is the function of です at the end of the sentence? Can it be omitted or changed?

です is the polite copula, giving the sentence a polite tone.
• In casual/plain Japanese you can replace it with だ: 電車は速くて便利だ。
• In very casual speech you might even drop the copula entirely: 電車は速くて便利。

Is it possible to reverse the order and say 電車は便利で速いです?

Grammatically, you could connect 便利 to 速い by turning 便利 into its て-form (便利で) and say 電車は便利で速いです. However, native speakers usually put the more ingrained or defining quality first. Also, 速くて便利です is the more idiomatic order when listing these two qualities.

Could I split this into two sentences instead of using the て-form?

Yes. You can say:
• 電車は速いです。便利です。
But using the て-form (速くて便利です) is more concise and natural when you want to link two adjectives in one statement.