This article presents a formal semantic account of the ambiguity associated with the -te iru construction in Japanese. This construction is known to receive at least two distinct interpretations: on-going process interpretations analogous to the English progressive and so-called resultative interpretations. The latter are sub-classified by some researchers into concrete result state readings and experiential state readings. Based upon the distributional properties of adverbials, we suggest that progressive interpretations of DURATIVE VERBS and concrete result state interpretations of INTANTANEOUS VERBS should be grouped together, as opposed to experiential readings of DURATIVE or INTANTANEOUS VERBS. To account for the distinction between these two types of interpretation, the proposed system analyzes the -te iru form into the morpheme -te, which is claimed to bear a perfect feature, and the aspectual auxiliary iru. Our proposal for the aspectual auxiliary iru is an extension of Landman's (1992) proposal and offers a unified account of the multiple interpretations of -te iru on the basis of a new analysis of INTANTANEOUS VERBS.