The purpose of this study is to primarily focus on the properties of the spatial ground, i.e., in/on the car/boat, which presents unavoidable difficulty to L2 learners. To conduct this study, a grammar test was created to elicit and measure participants’ knowledge of the English prepositions in and on with 51 intermediate-level 1st-year Japanese university students (as representative of L2 learners). The results suggest that differences in image schema between English and Japanese combined with family resemblance are the main causes of the difficulty. For example, the size of vehicle plays a prominent role in describing spatial relations in English; however, this is not necessarily applicable to other languages as these basic properties of figure and ground may not be universal nor are they self-evident. Pedagogical implications include explicit L2 instruction incorporating crosslinguistic differences in image schema for prepositional complements.