The impersonal or psyc-predicate construction in Old English (=OE) poses a special challenge for most case theories in generative linguistics. In the OE impersonal construction, the experiencer argument is marked by dative, accusative, or nominative, whereas the theme is marked by nominative, genitive, or accusative, or by a PP. The combinations of possible cases for experiencer and theme are not random, bringing about daunting complexity for possible and impossible case frames. In this paper, I develop a conceptual semantic case theory (a la Jackendoff 1990, 1997, 2002; Yip, Maling, and Jackendoff 1987) to provide a unified account for the complicated case frames of the OE impersonal construction. In the conceptual semantic case theory, syntax and semantics have their own independent case assignment principles. For impersonal verbs in OE, I propose that UG leave an option of determining either syntactic or semantic case to lexical items. This proposal opens a new window for the OE impersonal construction, in that it naturally explains both possible and impossible case frames of the construction.