(1) We observe people in a restaurant making choices from a literal menu of realizable alternatives.
The action that is taken by each and every diner in the restaurant is the only possible action in the instance that it is necessarily taken.
You are scrambling the context of actualities with the context of possibilities. They are like oil and water. They do not mix. You are free to use one or the other, and alternate between them, according to well established grammatical rules, but if you conflate their meaning you will destroy their meaning, and end up with nonsense.
Let me sort them out for you. Within the context of deterministic reality, we have people in a restaurant who are uncertain what they will choose for dinner. They face a menu of alternate possibilities and find that they must choose what they will order before they will get anything to eat.
They are initially uncertain as to what they will choose. So, they cannot yet tell the waiter "I will have this" or "I will have that". They simply do not know at this time what they will inevitably choose. They are uncertain about the deterministic reality of what they "will" do.
So, they leave the grammatical context of things that they will do and enter the grammatical context of things that they can do. Within the context of things they can do, they will think about different items on the menu that they might enjoy. Each item on the menu is something they "can" choose. But none of them are as yet something that they "will" choose.
Within the context of deterministic reality, what they will choose has not yet been meaningfully caused. No event is ever fully determined (caused to happen) until its final prior causes have played themselves out (and that play will not be over until the fat lady sings, "I will have the Chef Salad, please").
In the meantime, we are considering the steak and the salad. We "can" order the steak. We "can" order the salad. While considering the steak we recall that we had the bacon and eggs for breakfast and a double cheeseburger for lunch. So, we decide to order the salad.
Now, finally, we know for certain what we "will" do. We tell the waiter, "I will have the Chef Salad, please."
Note that we do not tell the waiter, "I
can have the Chef Salad". If we said, "I
can have the Chef Salad" the waiter would assume we were asking a question, and answer "Yes", and still wait for us to tell him what we
will have. "I can" and "I will" mean two entirely different things, and we need to retain those two distinct meanings.
So, when you say something like, "The action that is taken by each and every diner in the restaurant is the only possible action in the instance that it is necessarily taken", you are confusing what "can" happen with what "will" happen, and creating nonsense.
The nonsense is in suggesting that, in the context of deterministic reality, ordering the salad was the only "possible" action, the only thing that "could" have happened.
The only correct assertion we can make in the context of deterministic reality is that ordering the salad was the only "actual action", and the only thing that "would" happen under those same circumstances.
You see, it was causally necessary that, in the context of deterministic reality, we would enter the context of possibilities during the choosing operation. Within the context of possibilities there are always multiple possibilities and multiple things that we can do.
Within the context of deterministic reality, one cannot use the term "possibility" without immediately shifting to the context of possibilities!
Do you see this yet?
What you see are actions being performed. You have no access to, or awareness of the underlying process that brings people to that point in time and place, each performing their only possible action in each and every instance in time in a progression of determined event (we are talking determinism after all.)
But we do have access to that knowledge in a general sense. We know, for instance, that the brain is performing our decision making, and the brain is composed of neurons grouped into areas according to their specialized functions with the brain. And we know that these areas work together, in some fashion, to present itself to us and the world as a single person.
In the restaurant, we presume that each person has their own goals and interests, and their own reasons for the choices they make. And these goals, interests, and reasons reliably cause the choice they make, and what they end up telling the waiter to serve them for dinner.
Thus, their dinner orders are both reliably caused (deterministic) and reliably caused by them (chosen by them while free of coercion and undue influence, which is to say, a "freely chosen will").
By your own definition of determinism, no alternate possibilities exist for anyone at any given instance in time.
Not by my definition, but only by your own false assumption that, in coming to the single actuality, we never consider multiple possibilities. That is a false assumption, not justified by the facts of our deterministic reality.
We even observe groups of people making decisions together: legislatures, committees, clubs, parent-teacher associations.
There is a group decision making technique called "brainstorming", where everyone is encourage to suggest alternative possibilities, however strange, within a non-judgmental context, on the theory that even a crazy idea may spur a different idea that is actually practical.
That is how things actually work within our deterministic reality.
... determinism fixes all actions and all outcomes.
That's worse than nonsense. That is
superstitious nonsense. You've assigned causal agency to an abstract concept. No sir. You do not understand what determinism is really about. Only the actual objects and forces that make up the physical universe can cause events.
And, as to free will, determinism cannot claim that free will means "freedom from causal necessity". The notion of "freedom from reliable cause and effect" is paradoxical, because every freedom we have, to do anything at all, requires reliable cause and effect. It is a self-contradiction to require any freedom to be free of the very thing that every freedom requires. Thus, the notion of "freedom from causal necessity" is fundamentally irrational, paradoxical, and cannot be used as the definition for anything.
Free will can be
operationally defined as a choice we make for ourselves while free of coercion and other forms of undue influence. And this is the definition that is applied when assessing a person's moral or legal responsibility for their actions. It requires nothing magical, nothing supernatural, and makes no claim to any "uncaused" choice.
Free will is an ideological notion ...
Only if we stupidly define free will as "freedom from causal necessity". That, my friend, is an ideological notion. And, unfortunately, it is a notion held by many otherwise intelligent people. But, that's what a paradox can do, drive people crazy.
Determinism, when limited to making reasonable claims, and free will, when defined operationally and stripped of the irrational notion of "freedom from causal necessity", are compatible notions.
There is no freedom from natural causality,
And, fortunately, no "freedom from natural causality" is required by the operational definition of free will. All that is required is freedom from coercion and undue influence. Nothing more. Nothing less.