In this sentence:

Neko da kara desu.
Because it's a cat.

Why are the "da" and "desu" used at the same time? Logically, it should've been:

Neko desu kara desu.

Or in a casual conversation if we don't drop the last "da":

Neko da kara da.


  • "neko da kara desu" is "it's because it's a cat". Ignoring the issue of formality, your question is essentially the same as asking why in English we have "it's" in there twice.
    – A.Ellett
    Commented Jul 3, 2016 at 16:11

2 Answers 2


Basically, the casual form is ~だからだ and its polite form is ~だからです. e.g.


The から is a 接続助詞(conjunctive particle), definition #1 in デジタル大辞泉:

2⃣ [接助]活用語の終止形に付く。 1 理由・原因を表す。「もう遅いから帰ろう」 (attached to the predicative form of 活用語. 1. indicates a reason or cause.)

The から needs to be attached to the predicative form such as ~だ or ~する, so here you get ねこだから (not *ねこから), then you use a copula だ or です to end a sentence (though you can just say ~だから。 in casual conversation), so you say ねこだからだ or ねこだからです.

You don't say *ねこですからです because you wouldn't need more than one polite marker in one clause, I think...

  • because you wouldn't need more than one polite marker in one clause, I think... -- it's not clear for you?
    – Oskar K.
    Commented May 3, 2016 at 2:08
  • I can't say with 100% certainty that that's the reason... but at least, I can say that we don't repeat です or ます in one phrase like that.
    – chocolate
    Commented May 3, 2016 at 5:39

This is one of those funny nuance things. It's got little to do with grammar and more to do with how it feels to say that. If I wanted to sound condescending I'd say it like that, though I guess to get that effect tone of voice is also important.

You would never in a million years say desukara desu. That just doesn't work. 9 times out of 10 you would just say neko dakara. Nothing more.

  • 1
    I know. My question is why.
    – Oskar K.
    Commented May 1, 2016 at 15:49

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