  Nevertheless, a great deal of human action has a richer psychological structure than this. An agent performs activity that is directed at a goal, and commonly it is a goal the agent has adopted on the basis of an overall practical assessment of his options and opportunities. Moreover, it is immediately available to the agent's awareness both that he is performing the activity in question and that the activity is aimed by him at such-and-such a chosen end. At a still more sophisticated conceptual level, Frankfurt [1988, 1999] has also argued that basic issues concerning freedom of action presuppose and give weight to a concept of ‘acting on a desire with which the agent identifies.’ Under Frankfurt's influence on this point, a good deal has been written to elucidate the nature of ‘full-blooded’ human agency, whether the notion is finally delineated either in Frankfurt's way or along different but related lines [see Velleman 2000, essay 6, Bratman 1999, essay 10]. Thus, there are different levels of action to be distinguished, and these include at least the following: unconscious and/or involuntary behavior, purposeful or goal directed activity (of Frankfurt's spider, for instance), intentional action, and the autonomous acts or actions of self-consciously active human agents. Each of the key concepts in these characterizations raises some hard puzzles.