This paper investigates an approach to human-computer interaction - actability theory - that emphasises human-via-computer-to-human interaction. This social action approach to HCI is confronted with affordance theory by Gibson; an ecological theory of perception. The notion of affordance is compared and related to actability. Different IT usage situations described in actability theory are critically examined. A re-conceptualisation of these situations is made and this refined conceptualisation is used to classify different usage situations of a municipal case coordination system as a small empirical illustration and test. In the last part of the paper, the definition of an actable IT system is revised. The IT affordances of different IT usage situations are clarified.