THE NATURE OF THE WILL
Not Libertarian Freedom. Some theologians argue that we are free to choose A or B for the *same* set of reasons or causes. This is called "contra-causal" freedom. For example, let's say you're standing at an ice cream stand and you're trying to decide between chocolate and vanilla. If we freeze time at the moment right before you make your choice, Libertarian freedom says that in that moment, and for the same set of reasons or causes, you can choose either chocolate or vanilla. But the problem with this view is that there is no determining or moving cause which leads you to choose either chocolate or vanilla. The fact that the will, on this view, is not determined, creates several problems.
First, how could such a will ever choose at all? If there is no moving or determining cause, there is no explanation for why it chooses one thing over the other. It seems like it wouldn't actually choose anything.
Second, how could such a will ever be held responsible for its choices? Our example of choosing a flavor of ice cream doesn't have ethical ramifications. But, in cases of moral choices, such as whether to lie or not to lie, how could a libertarianly free will be held responsible? The person who has a libertarian will might complain to God on judgment day: "I often wished my libertarian will would choose other than it did, but it often chose against all causes and reason, including my own character and reason. I shouldn't be held responsible for it."
Third, how could such a will be called "free?" A random-choice-generator that is capable of choosing A or B apart from and against all determinative causation and reason doesn't strike me as free at all. It's a jerky mechanism that often erupts in random directions. This is not freedom, but slavery.
Compatibilistic Freedom. Compatibilistic freedom says that determinism is compatible with freedom. This is the biblical view of freedom, and it's much easier to explain. Compatibilistic freedom is the teaching that our wills necessarily choose what we want most at any given moment. Our choices flow from our minds and hearts. Our wills are *determined* by what our minds believe will be best at the time of our choice. We may have competing beliefs and desires within us, but the thing we *believe will most satisfy us* is the thing we will always choose. Thus, our hearts determine our choices and behaviors, and this determinism is compatible with true freedom.
Matthew 12:35-36 says, "The good person out of his good treasure brings forth good, and the evil person out of his evil treasure brings both evil. I tell you, on the day of judgment people will give account for every careless word they speak." Notice that the heart produces/determines/causes the choices. This is the basis of responsibility and divine judgment. Determinism doesn't undermine responsibility or freedom; rather, it grounds it.
Similarly, Matthew 15:18-19 says, "But what comes out of the mouth proceeds from the heart, and this defiles a person. For out of the heart come evil thoughts, murder, adultery, sexual immorally, theft, false witness, slander." So, the heart determines our choices. And, freedom and responsibility are consistent with such determination.
THE FREEDOM OF THE WILL
Natural Freedom. In order for the will to be naturally free, it must not be naturally hindered. It has to have the capacity to function as it was designed. Here's what that means. Your will can function freely, if it is not hindered by internal or external natural obstacles.
For example, if I pump you full of drugs, which make you hallucinate and believe things that aren't true, then you are going to choose to do some crazy things. But, you aren't acting freely because a foreign agent, the drug, is messing with your head. You are rightly not held responsible for what you do if I'm the one who put the drugs into you. You are not naturally free.
Here's another example. Let's say I tied up your hands and feet at work and then proceeded to steal from your employer right in front of your face. If you were untied, then you would be responsible to try to stop me. But, since you are tied up, you physically can't stop me from stealing. You are not free, and as a result, you are not responsible for your failure to stop me from stealing.
Natural freedom is the natural capacity to choose what you want most without natural hinderances. Babies, brain damaged people, people with dementia or other crippling illnesses are not naturally free; therefore, their responsibility for their actions is mitigated.
Moral Freedom. Moral freedom is the freedom to choose what is morally right. In the garden of Eden, Adam had moral freedom. He had the ability not to sin and he had the ability to sin. But, when Adam sinned and fell, he and all who descend from him by natural generation, have lost the ability not to sin. Everyone in Adam has lost moral freedom.
This is what Romans 3:11-12 teaches. "No one understands; no one seeks for God. All have turned aside; together they have become worthless; no one does good, not even one." Our minds "understanding," our hearts "seeking" and our wills "doing good" are all fallen. Those in Adam have all lost the moral freedom to do what is good.
But, in Christ, by His Spirit, we regain the ability not to sin. Christians have moral freedom, but not completely. We have freedom not to sin and the freedom to sin, but there is a conflict within us, unlike Adam. Two principles are constantly at war within us and it is impossible on this side of heaven for us to eradicate all sin. That's why Paul says in Galatians 5:17, "For the desires of the flesh are against the Spirit, and the desires of the Spirit are against the flesh, for these are opposed to each other, to keep you from doing the things you want to do." As believers, part of us wants to obey Christ, and another part wants to sin. Sometimes we want to sin more than we want to obey. Other times we want to obey more than we want to sin. Whichever desire is greater is the desire we follow at any given moment. The greater desire is always the one we *believe* will satisfy us the most at the time. The Christian is in a war to believe that Christ is better than sin, though sometimes we believe the lie that sin is better than Christ.
Finally, when Christians die and go to heaven, they will regain full moral freedom. They will lose the ability to sin. And, they will only have the ability not to sin. This is total freedom. It is freedom from the lies of the devil. It is freedom from sin.
Some people strangely argue that if an agent is truly free, then he has to have the freedom to sin. But, that's odd, since God doesn't have the freedom to sin. It is impossible for God to sin, yet God is surely free. The saints in heaven don't have the freedom to sin, yet they are free too. Therefore, freedom to sin can't be the essence of moral freedom. Rather, freedom from sin is the essence of moral freedom.
So, there you go. When speaking of the the human will, we need to talk about the nature of the will (whether it is libertarianly free or compatibilistically free) and we need to talk about the freedom of the will (natural freedom vs moral freedom). Hope that helps!