This paper describes a computational model which is geared towards providing helpful answers to modal and hypothetical questions in knowledge base systems (KBSs). The model is an essential component of a more complete model which aims at giving helpful answers to questions presented in a natural language. The overall work touches on formal semantic theories on modality and question answering (which have been mainly addressed by linguists and semanticists), intensionality, partiality and belief revision. In this paper, we shall mainly be concerned with the question of partiality where we present a three-valued logic, to which we shall refer as K-T, for reasoning with incomplete information and a proof method for the logic. Along the way, we shall lightly touch on other issues such as answerhood, modality, context and helpfulness.