The possibility that defendants may plead that, through no fault of their own, they lacked the capacity for free agency at the time of the alleged offence, raises the most fundamental issues of principle in the criminal law. The recent decision in R. v. T gives fresh impetus to a full discussion of those issues. In the course of this article we will see that the law is ill-equipped to deal with the full variety of kinds of involuntary lack of capacity, as I shall call it, that ought wholly or partially to excuse. In this the law is hampered by the partial and ill-defined character of its understanding of how people identify harmful conduct for which they were (not) responsible, and by the related fact that it can deal with involuntary lack of capacity only through the blunt instrument of acquittal on the grounds of insane or non-insane automatism. Through enriching the theoretical underpinnings of the law's conception of the scope for pleas of involuntary lack of capacity, and giving the judiciary a more sophisticated armoury of remedies to deal with them, it is in fact possible to sift out the deserving from the undeserving amongst such pleas in accordance with workable principles.