The fact that they say "I can´t" suggests to me that they have already tried - unsuccessfully.
So I am assuming that their internal restriction is just as severe an obstacle as an external restriction would be.
I'm inclined to believe that this is rarely the case. And of course there are gradations of trying.
If the internal restriction is nothing more than the belief that they cannot then while it may be as severe it is still self imposed, and could be overcome if the belief structure were different. If this is not the case, then the belief is not what is primarily restrictive but simply a recognition that there is in fact something else restricting their actions.
The thread title and the OP should have given away that I am neither approaching this in an ontological nor epistemological manner.
It´s not like I think there is freedom and we have to detect/define what it is.
I was merely contemplating on the use of a word.
Forgive me, quatona, but no definition can be purely semantic. The way we use words is to refer to realities. Moreover your definition involves belief formation so it is of necessity epistemological. If you do not believe that our word refers to anything, then it does not matter. However your response above does suggest that you think it refers to something. You seem to think there are capacities to act and restrictions upon them and a lack of said restriction. Even so, the way we typically use 'freedom' is to refer to the ontological capacity to do something and not the perception of whether or not one can do it and the conversation you have been having bares that out. If what you are really saying is that feeling as though you cannot do something makes you unable to do it then you your self recognize that being unable to do something is really what you are getting at. And while belief formation as to whether something is possible can create possible restrictions, it is not the only possible. restriction. Your definition suggests this, and GrowingSmaller pointed this out. Your addition of the word "only" does not fix this situation but worsens it.
Additionally while I admit that typically as we use freedom only conscious agents are capable of it, and belief formation with regard to capacity is something which conscious agents will probably always be able to form, it still does not seem that this belief formation is anything but accidental to freedom itself. It may be essential to freedom that it be done by conscious agent and essential to conscious agents that they hold these beliefs but it is accidental to freedom that conscious agents hold this belief because, I assume, it is their volitional aspect which is relevant to their capacity to act freely and this has no direct part in their belief formation for our purposes.
Anyway, the point that I was trying to make is that typically freedom is considered something like "A capacity to do something without restraint." And the question of free will comes into play when someone questions whether or not one can actually do anything other than what one's nature determines. The denier of free will claims that despite feeling as though you can do x or ~x you can in fact only do x. Defenders of free will often claim that the fact that I feel I can do x and ~x is evidence that I can. You seemed to try to side step the question by making the defenders epistemological claim the reality itself. I know that was not your intention when making the post, but assuming you were formulating your opinion on the basis of the established debate, I thought that historically you may have still made this mistake.