  Information about the powers and abilities of acting entities is used to
coordinate their actions in societies, either physical or digital. Yet, the
commonsensical meaning of an acting entity being deemed able to do something is
still missing from the existing specification languages for the web or for
multi-agent systems. We advance a general purpose abstract logical account of
evidence-based ability. A basic model can be thought of as the ongoing trace of
a multi-agent system. Every state records systemic confirmations and
disconfirmations of whether an acting entity is able to bring about something.
Qualitative inductive reasoning is then used in order to infer what acting
entities are deemed able to bring about in the multi-agent system. A
temporalised modal language is used to talk about deemed ability, actual
agency, and confirmation and disconfirmation of deemed ability. What
constitutes a confirmation and a disconfirmation is left to the modeller as in
general it depends on the application at hand. So to illustrate the methodology
we propose two extended examples, one in practical philosophy, the other in
system engineering. We first use a logic of agency and ability to obtain a
version of Mele's general practical abilities. Then, we look at the management
of abilities in a supervised system.
