It has been held in various forms. In its extreme form it maintains that the individual is absolutely free to chose this or that action indifferently (the liberum arbitrium indifferentiae), but most libertarians admit that acquired tendencies, environment and the like, exercise control in a greater or less degree.
Although he denies liberty to the will in this sense - indeed, strictly speaking, neither liberty nor necessity, he says, is properly applied to the will, " for the will itself is not an agent that has a will " - he nevertheless insists that the subject willing is a free moral agent, and argues that without the determinate connexion between volition and motive which he asserts and the libertarians deny, moral agency would be impossible.
The great advance of biological knowledge in recent times though it has in no sense created a new problem (men have always been aware of the importance of racial or hereditary physical qualities in their influence upon human conduct) has certainly rendered the existence of complete individual freedom (in the sense in which it was advocated by older libertarians) in the highest degree unlikely.
But, nevertheless, the new light thrown upon the unity of the self and the more careful and accurate scrutiny made by recent psychologists of the phenomena of decision have rendered it no longer possible either for determinists to deny the fact of choice (whatever be their theory as to its nature) or for libertarians to regard the self or the will as isolated from and unaffected by other mental constituents and antecedents, and hence, by an appeal to wholly fictitious entities, to prove the truth of freedom.
If, how ever, it be argued by libertarians that no explanation is possible of the manner in which the self or the will makes its decisions and inclines to this motive or to that, while they still assert the independent existence of the self or will, then they are undoubtedly open to the retort of their opponents that upon such a theory no rational explanation of conduct will be possible.