Imagine the following conversation:
Waiter: What would you like for the main course?
Customer 1: I will have the squid.
Customer 2: I am an eel.
In English, this makes no sense, unless Customer 2 is actually an eel, which seems unlikely. Japanese, however, has a construction that can be literally translated as though the speaker is declaring that they are an eel. This is called the “eel sentence”.
An eel sentence (or unagibun in Japanese) is a sentence of the format “X wa (topic marker) Y da (copula)”. This format, in its most basic use, can be translated as “X is Y”. However, in the case of an eel sentence, this meaning does not apply. Therefore, a customer in a restaurant might say: “Boku wa unagi da”, with X = boku (“I”) and Y = unagi (“eel”). But rather than intending to say that they are an eel, the customer here means that they will have it for dinner.
The term unagibun was coined by Keiichirō Okutsu in 1978, and since then it has been used by many linguists and featured in Japanese language textbooks. Of course, the word “eel” can be substituted by almost any other noun depending on the context, but since “eel” was the example originally used by Okutsu the term “eel sentence” stuck.
If you would like to read more about eel sentences, see the articles listed in the bibliography below.
Editor of Brill’s Linguistic Bibliography
Koya, Itsuki: Shitei unagibun to “NP1 no NP2” ni tsuite. – Reports of the Keio Institute of Cultural and Linguistic Studies 45, 2014, 227-238 | The specificational “eel” sentence and its relation to the “NP1 no NP2” construction.
Obana, Yasuko: Unagi-sentences in Japanese and mutual knowledge. – Journal of pragmatics : an interdisciplinary monthly of language studies 33/5, 2001, 725-751.
Yagihashi, Hirotoshi: Why can a Japanese unagi-sentence be used in a request? – Lodz papers in pragmatics 5/2, 2009, 227-240.