csbrown28 said:
To say that there is something called "free will" is to suggest that there is a state in which a person can lack free will.
Why is this? Sub in "identity conditions" or "essential properties" for "free will" in the above. To say that there is some X doesn't necessarily imply that possibly there might not be some X. Free will might be an essential property of persons, in which case, a person could never lack free will, and the very concept of a person lacking free will would be absurd. This is not to say that free will is an essential property of persons; only that I don't see why you think saying there exists some X is to suggest that X might not exist.
I think most people are confused on the topic of free will. When most people use the term "free will," what they really mean to invoke are at least one, and sometimes both, of two concepts:
1. Freedom of action
2. Will as a causal force which is neither determined by natural laws nor a result of indeterminate or random processes.
So, say I have a will whose object is X. To say I have free will is then to say that either: 1. I am free to act so as to proceed to X, and, 2. my will to X cannot be calculated by something like LaPlace's demon. That is, at least possibly, my will to X could never be predicted no matter how much physical information is known prior to the existence of my will to X. Or, it could be to say both 1. and 2.
csbrown28 said:
If someone did not have free will, can you tell me how exactly would that person differ from a person who did?
There would be at least one of two differences.
First, there are people who suffer a kind of brain damage that leads to locked-in syndrome (I have no idea if that's the real name for it, but it's an intuitively evocative name). To all appearance, the person is a vegetable. But in fact, their mental life goes on as before; they're simply in a body which has no capabilities for willed action of any kind. Such a person has no freedom of action.
(As an aside, I take it that very few people are ever completely locked in. Usually such people have the ability to communicate by blinking, raising a single finger, or some such. We have inferred, based on the commonalities of the brain damage between cases, and information gained via fMRI scan, that being totally locked in is possible, and may have occurred in a few cases).
Second, if we ever are able to reliably calculate what a person's will is based on prior knowledge of relevant physical information, that person lacks free will. It's possible that no persons have free will thanks to this always being a possibility. However, lacking any evidence that this is the case (i.e. that will is determined by physical laws), it's a difficult case to make.