The English even is known to evoke a scalar presupposition that the relevant proposition is the least likely one among the alternatives. However, in a downward entailing context, we obtain the opposite presupposition that the relevant proposition is the most likely. One theory holds that the ambiguity is due to the scope interaction between even and a downward entailing operator (Kartunnen and Peters 1979). The other theory holds that even is lexically ambiguous between a regular even and a negative polarity even (Rooth 1985). This paper compares the two theories by examining novel data from Japanese even items (-mo 'also, even', -demo 'even', and -dake-demo '(lit.) even only'). The author argues that the scope theory is better suited for the Japanese data, and presents a compositional analysis of the even items under the scope theory (à la Lahiri 1998, Guerzoni 2003). In particular, the distribution of the even items is explained by the scope interaction between even, only, and a DE operator. The proposed analysis further accounts for the distribution of some negative polarity items in Japanese.