In Irish one finds a range of silent arguments (subjects of finite clauses, objects of nonfinite clauses, prepositional objects, and possessors) whose presence is signalled by inflectional morphology on governing functional heads. The interaction between the inflectional marking and the silent argument (always clearly pronominal) involves not just the familiar array of person and number features but also a certain kind of impersonal element, at least roughly analogous in its interpretation to French on, German man, Swedish man and so on. This talk is part of an ongoing effort (dating back to a joint paper with Ken Hale in 1984) to better understand these interactions in the context of recent work on the (mis-named) `Null Subject Parameter'.