Michael McKennaMichael McKenna is a compatibilist and naturalist who is a prominent defender of Harry Frankfurt's attempts to deny the principle of alternative possibilities (or PAP). McKenna's recent attempts are notable in that they openly grant libertarian freedom involving alternative possibilities. John Martin Fischer described any remaining alternative possibilities as miniscule "flickers of freedom" that are not morally significant. McKenna argues that Frankfurt defenders should not struggle to block these many alternative possibilities that are not morally significant. They should grant indeterministic libertarian freedom to those and concentrate on blocking the morally significant. McKenna extends Fischer's morally "robust" alternatives, saying that they must figure in the ground upon which an agent is morally responsible for her action. McKenna hopes for a strategy that will not simply discount all the alternative possibilities, because that might appear to be determining the agent's action.
Can Frankfurt examples achieve both the results of polluting all robust alternatives and at the same time not presupposing determinism? The trouble seems to be that effectively polluting all alternative actional pathways within an agent's control comes dangerously close to making that problematic deterministic assumption. But loosening the restraints so as to avoid this problem seems to invite sufficient slippage that the incompatibilist will be able to locate some robust alternative. I suggest that the Frankfurt-defender attempt to close off all morally significant alternatives without attempting to pollute all alternative actional pathways within an agent's control. To do this a Frankfurt-defender must identify some class of actional pathways comprising morally insignificant alternatives — alternatives that could not aid in grounding the judgment that an agent in a Frankfurt example is morally responsible for what she does. The Frankfurt defender can leave these actional pathways entirely open and within the control of the agent. No fancy gizmos or crafty interveners need to be present to achieve the modest ensuring conditions required simply to close down some, but not all, alternatives. It is easy to imagine contingencies entirely consistent with indeterminism in which some range of an agent's options are blocked. Call this the limited blockage strategy for defending Frankfurt examples.With his "limited blockage strategy" McKenna can allow "oodles and oodles" of unimportant alternatives.
The theoretical advantage the limited blockage strategy offers over other recent Frankfurt example strategies is that limited blockage cases openly grant libertarian freedom involving alternative possibilities. The examples. therefore, clearly do not require any special considerations that might tacitly import a deterministic relation between agent and action. Indeed, they allow an agent in a Frankfurt example oodles and oodles of alternatives. lmagine in the case Brain Malfunction, the many further possibilities open to Casper. Casper could have sung a little ditty and done a cutesy jig like Shirley Temple, finishing off with a set of jazz hands; or begun citing nursery rhymes; or made an attempt to eat his fist; or any of a number of equally ludicrous and irrelevant things.