Determinism: given the state of the world at any moment in time, there is only one way it can be at the next moment.
That is figuratively correct, but literally false. To make it literally correct, replace the "can" with "will", as in "there is only one way it will be at the next moment".
But it is literally correct. That it is literally correct is supported by the terms and conditions of determinism.
As all events proceed without deviation, fixed by antecedents, this condition negates the possibility of alternate actions. Where there are no alternate actions, nothing other than what has been determined to happen can happen.
Everything that happens is fixed. There is no change in the sense that something else could have happened.
The system is of course in constant change.
Each and every state of the system as it evolves is as it must be. Including the brain and the thoughts and actions it produces. Not through free will, but entailment.
Defining free will as an action performed without force or coercion is not adequate because all determined actions proceed as determined without restriction.
Apparently, what is "adequate" for the compatibilist is "inadequate" for the incompatibilist. But only the compatibilist gives an adequate description of reality. The incompatibilists want us to get lost in their delusion that one must be free of causal necessity in order to be free at all.
What is or isn't adequate to qualify as free will is determined by the given description of the nature of determinism, and not by a definition that ignores or neglects a key element in the formulation of that definition.
Could have, would have, might have
''The compatibilist readily admits that if determinism is true, then we clearly do not have physical alternatives open to us. But this does not matter, he says, for what really matters is that we have the right sort of alternatives open to us, and these are not physical alternatives.''
Not being physical alternatives, 'could have, would have, might have' is totally irrelevant to the argument and the given definition of determinism.