The paper is about the logic of expressions of the form `agent x brings
it about that A is the case', or `agent x is responsible for its being the
case that A', or `the actions of agent x are the cause of its being the
case that A'. Agents could be deliberative (human or computer) agents,
purely reactive agents, or simple computational devices. The `brings it
about' modalities are intended to express unintentional, perhaps even accidental,
consequences of an agent's actions, as well as possibly intentional
(intended) ones. Since we make no assumptions at all about the reasoning
or perceptual capabilities of the agents we refer to this form of agency as
`unwitting'; unwitting can mean both inadvertent and unaware. The semantical
framework is a form of labelled transition system extended with
an extra component that picks out the actions of a particular agent in
a transition, or its `strand' as we call it. We de ne a modal language
for talking about the actions of individual agents or groups of agents in
transitions, including two de ned modalities of the (unwitting) `brings it
about' kind. The novel feature is the switch of attention from talking
about an agent's bringing it about that a certain state of a airs exists
to talking about an agent's bringing it about that a transition has a certain
property. The middle part of the paper presents axiomatisations of
the logic, and comments on relationships to other work, in particular on
resemblances to P orn's (1977) logic of `brings it about'. The last part
is concerned with characterisations of (unwitting) collective agency, that
is, the logic of expressions of the form `the set G of agents, collectively
though perhaps unwittingly, brings it about that A'.