One of the perennial vexing questions humans have asked themselves for millennia is: do we have free will? Essentially there are three answers. No, we do not have free will; all our actions and thoughts are part of a deterministic universe of inescapable cause and effect. Sort of; even though the universe is one long causal chain of which we are inescapabely a part, there is an intution we have that our thoughts and decisions, though not free of the causal chain, can, in some way, be our own, and therefore our responsibility. And, Yes, there is free will that is undetermined by any antecedent causes.
Determinism is that understanding that the pervasive cause and effect relationships which we note in the material/physical universe we inhabit obtain at all times in all places on all things, including humans and their thoughts, decisions, and actions. Hard determinists (such as B. F. Skinner) would hold that this means free will is a chimera, and has no reality. There are not very many commited hard determinists around. Instead most determinists are "soft" determinists. Soft determinists (normally called compatibilists) would not deny the inescapable causal chain of which we are a part, but would, through philosophical analyses, argue for and show how it is that our determined choices and actions are still things for which we can be held responsible. Libertarians (sometimes called incompatibilists, though this label fits hard determinists as well) assert that the cause and effect chains of the universe do not hold for human acts, that in some way our decisions are free of causation (except the cause of volition).
So the arguments regarding free will--at least in the Anlgo-American/analytical philosophical tradition--usually pit compatibilists (soft determinists) against libertarians. Compatibilists frequently object to libertarian conceptions of free will on the grounds that either a) free will is based on an intuition that to be responsible for our actions there must always be a possible alternative act, and/or b) that if there are no antecedent causes for our actions, then free will is subject to the charge of arbitrariness and can offer no real metaphysic of volition and action. Libertarians often object to compatibilist conceptions of moral responsibility within the constraints of determinism on the grounds that a) there is an inbuilt and question-begging presumption of the indentification of mental and physiological processes (the brain is the mind, and vice versa), and/or b) the compatibilist account charge of arbitrariness assumes a metaphysic which itself gives rise to the charge of an incoherent account of volition.
The difficulty one has in arbitrating these positions is that both speak to strong intuitions and experiences. On the one hand we do experience the universe as a system of cause and effect. And this is not just a consistent experience. It is an inviolable one (or, for certain worldviews, such as the Christian one, almost always inviolable). If we walk into our living room and observe that the flower pot has fallen from the window sill to the floor, we immediately extrapolate to an antecedent cause. And if the cat looks sufficiently guilty, we make the appropriate connections.
On the other hand, we have the same pervasive experience that we are the authors of our actions. And not just the authors, but we intuit a direct causal obligation between our choices, actions and the responsibilities for the consequences of those choices and actions. Indeed, this understanding of free will is embedded in our social and juridical systems. If there is set in front of me a Macallan 18-year single malt and a Bud Light, I not only have an inescapable intuition that my choice of the robust highland Scotch over the "having-sex-in-a-canoe" beer is a free one, undetermined by any physical/material causes, but my experience is thoroughly one of making a conscious selection based on various criteria presented to my mind.
Another of the difficulties is that the compatabilist and the libertarian seem to be arguing from opposite ends of the volition act. The compatibilist looks at an act and says, "Here are the antecedent causes. You chose the Scotch not from free will, but predetermined dispositional factors of heredity, nurture and experience." The libertarian looks at a set of choices and says, "I am utterly free to choose one or the other alternative." The libertarian cries, "Foul," at the compatibilist "reading back" into an act a determinist set of causes. The compatibilist cries, "Illusion," at the libertarian positing of alternative possibilities.
The compatibilist, however, not only needs to develop a more robust account of volition, but in that account must set the basis for predictive accounts of human acts. That is to say, precisely because the universe is ordered in cause and effect relationships, we can count on various processes happening in the same way. We can know that if we light a fire in the living room, then entire house will be in danger of burning to the ground. We can know that if a certain dosage of morphine is injected into the human body, that respiration will shut down and the person will die. The compatibilist will affirm that we can, indeed, make predictions about human behavior; this is what the social sciences can accomplish.
Furthermore, the compatibilist presumes a certain identification of mind with brain. That is to say, for the compatibilist mental processes are merely brain functions. The physiological processes that affect the brain, then, also affect the mind, and therefore our mental acts. Thus the causation of our mental acts are precisely the material causal chains which obtain in the universe.
But conclusion that human behavior is predictable, therefore it is determined, is a weak claim. While there is that about human behavior which can be liable to prediction, it is not the same level of predictability that one gets when positing that the sun will rise tomorrow, that ice cream will melt on a hot summer sidewalk, and that at sea level water will boil at a certain temperature. In short, the determinism of human actions lack the sort of predictibility which one can assume of naturalistic causes. The compatibilist will argue that we lack the ability to predict human behavior with the same accuracy as other material events only because human actions are infinitely more complex than these other events. If we were to more fully understand the causal chains which constrain human thoughts and actions we would also be able to more accurately predict those thoughts and actions. But this is not an argument.
While the compatibilist can give a positive account of human volition--we will to do and do certain actions because of the inescapable causal chains--the libertarian's account is largely a negative account. The libertarian asserts that we are not determined. Our choices and the acts resultant from them are free and unconstrained. But there does not seem any sort of explicable paradigm--aside from the assertion of free will--that the libertarian can give. The libertarian may well assert that the simplest account is the more accurate. Or may similarly assert that there is no obligation to provide an explanation for free will; rather, to posit it with evidenciary claims. But neither is this an argument.
While the compatibilist is clearly subject to the charge of making a category mistake by conflating brain with mind, the libertarian must give some account of how it is that mind is different, if not separable from brain. Here the libertarian can be helped by Aristotle's De Anima. The soul, Aristotle notes, is affected by the body, and it is inseparable from the body, but it is not the body. It would seem the libertarian understanding of free will can be helped by this account. The compatibilist may well complain that if Aristotle's mind is affected by and inseparable from body, then it must be determined and therefore mind's acts are determined by the causal chain in which body is immersed; either that or an irresolvable dualism obtains, in which case a third bridge must be built that mind may be a cause for body's acts.
This summarization is intended to note the difficulty of the issue of free will. Moral responsibility is no less complex, though may be more quickly stated. The libertarian will assert that it is precisely because we are the authors of our acts (arising from causal mental states) that we can and ought to be held responsible for them. If our acts (and the choices antecedent to them) are merely the most recent links in the causal chain then we can hardly be held responsible for them in any meaningful way.
The compatibilist will argue that if there is a case in which there is no other alternative to the way we must act, yet can or ought to be held responsible for that act, then it follows that it is plausible to assert moral responsibility in the face of determinism. One set of accounts often given is that of Frankfurt-style examples in which regardless of what an agent chooses or decides to do, he will be constrained to a particular action. If he decides to do something other than, say, killing a man, some sort of constraint (a special device put in the brain, say) will set in motion those causal things necessary to to ensure that the agent kills the man. So the agent either decides to kill the man, and does so, or decides not to kill the man, but is nonetheless constrained to do so. He has no other option than to kill the man. His act is utterly determined. Yet in one instance we hold the agent morally responsible for the act and in the other we do not. Thus, say the compatibilists, moral responsibility is not negated by determinism.
The libertarian would insist that the precise difference between culpability and innocence in the preceding account, is that of decision. It is precisely the free decision which makes an agent culpable for that act. Though the agent was absotluely constrained to kill, guilt entailed upon the agent's decision to kill.
This brief account can hardly do justice to such a complex matter, and the resolution of the problem, if indeed there is one, will come not from within the compatibilist or libertarian paradigm.