質問: フェイ、まだ、そうと判明した訳では。違う原因かもしれない。 Is it short for 訳ではない?
回答: Yes, this means そうと判明した訳ではない. You may know the omission of ない can happen frequently with negative polarity items such as ちっとも, 決して, 少しも, and どこにも. Likewise, people know 訳では is almost always followed by a negative predicate (i.e., ない), and thus the predicate can safely be omitted in casual conversations. Note that this は is critically important to indicate something negative will follow. See: Why is the topic marker often used in negative statements (ではない, ~とは思わない)? Examples: > > * ハサミ? それでは...。 Scissors? I doubt it helps... > * 明日はちょっと...。 Tomorrow is, well, ... (inconvenient for me...) > * 「見たい?」「そ、そんなことは!」 "Wanna see it?" "N-No, I...!" > > >