"As a general rule, the potential form of verbs, which is a stative predicate, cannot be used with the stative descriptive teiru. However, in actually, such expressions often appear in conversational Japanese. In written text, with the exception of direct quotations from conversation, these expressions are almost completely absent. Thus, this study examined both the ability-related meaning of ‘potential-form +teiru’ and teiru itself to investigate the environment in which each expression appears, the implications of the expressions, and the reason for their tendency to be used only in conversational Japanese. The study results revealed the following three properties of ‘potential-form + teiru’: 1. It acknowledges the actualisation of a certain state through the actions of the subject. 2. That state implies a Positive evaluation of an expected way of being. 3. As it describes the resultant state of the subject’s actions, the content of the positive evaluation is not specified. These properties reveal that the information transmitted by the expression has a tendency towards ambiguity unless its implications are limited by adverbial phrases or by the situation of speech. It is for this reason that it is not used in reports or other context that demand greater objectivity. "