Morality, Kant says, cannot be regarded as a set of rules which prescribe the means necessary to the achievement of a given end; its rules must be obeyed without consideration of the consequences that will follow from doing so or not. A principle that presupposes a desired object as the determinant of the will cannot give rise to a moral law; that is, the morality of an act of will cannot be determined by the matter or content of the will for when the will is materially determined the question of its morality does not arise.
This consideration leads Kant to one of his most important theses. If the moral character of willing is not determined by the content of what is 
willed, it must be determined by the form:” If a rational being can think of his maxims as universal laws, he can do so only by considering them as principles which contain the determining ground of the will because of their form and not because of their matter”. Therefore, the morality of a maxim is determined by its functioning as a universal law, applicable as a general rule to every rational agent.
Since a moral will must be so in virtue of its form alone, the will must be capable of a purely formal determination; that is, it must be possible for a man to act in a certain way for the sole reason that willing in this way is prescribed by a universal law, no matter what the empirical results will be.
A will to which moral considerations apply must be, in the strictest sense, a free will, one that can function independently of the laws of natural causality. The concept of morality, therefore, has to be explained in terms of a universal moral law, and the ability to will in obedience to such a law leads us to postulate the freedom.
The freedom which Kant is talking about, is not only a negative freedom consisting in the absence of constraint by empirical causes, it is also a positive freedom which consists in the ability to make acts of will in accordance with the moral law, for no other reason than that they are in accordance with it.
Freedom, in this sense, corresponds to Autonomy of the will and its absence ( any situation in which the will is determined by external causes ) is called Heteronomy.
In obeying the moral law for the sake of the law alone, the will is autonomous because it is obeying a law which it imposes on itself.
In the third section of the “Grounding for the Metaphysics of Morals”, Kant answers the problem of the possibility of the Categorical Imperative. Is the problem to be understood as if the Categorical Imperative is possible, or how it is possible?
In the “Critics of Pure Reason”, the problem regarding the synthetic a priori judgments concerns just the modality in which they can be applied. The fact that they are actually possible is proved by the synthetic a priori judgment contained in sciences as mathematics and physics which are trustworthy sciences.
Metaphysics, however, is not a reliable science and, therefore, Kant suggests that we should look not only for the modality in which they can be applied, but also for their reliability. Similarly, the Metaphysics of Morals must prove the validity of the moral imperative. As Paton suggested, Kant tries to show not only how the Categorical Imperative is possible, but also that it is possible.[” Furthermore, we have not asserted the truth of this proposition, much less professed to have within our power a proof of it. We simply showed by developing the universally accepted concept of morality, that autonomy of the will is unavoidably bound up with it, or rather is its very foundation” par. 445].
The condition for the possibility of the Categorical Imperative is Freedom.
The third section contains a demonstration of Freedom which Kant tries to derive by means of excluding at least other two ways.
A first would be to assert that Freedom is experienced by us, that it is sensed, but this is not the truthful one, because experience would be the one of my personal freedom and Kant wants to demonstrate that every rational being is free , in order to infer that every rational being must obey the Categorical Imperative.
A second way would be to show that every rational being has at least the idea of Freedom, i.e. he is convinced to act according to reason, not only under instincts; he is persuaded to act in this way, because he sees that acting this way is right, because he is determined by his reason and not only by blind instincts. But, if a rational being had the idea of freedom, but were not really free, he would be mistaken even about his reasonableness; he would think he were acting for some reasons, whilst he would actually be like a robot. But, as we saw before, being aware of being rational means being aware of the necessity of acting in accordance with a law , and what we are trying to do is to justify this necessity.
Surely, if we consider ourselves to be free, we acknowledge ourselves obliged to follow the moral law, and if we consider ourselves obliged to follow the moral law is because we think of ourselves as free. But there seems to be a vicious circle because, until now, it has been demonstrated neither that we are obliged to follow the law, independently from the conviction of being free, nor that we are free, independently from the belief of being subject to the law.
We still have to prove that the Categorical Imperative is possible.
There is still a way open to us: ” To inquire whether we do not take one point of view when ,by means of Freedom, we think of ourselves as a priori efficient causes, and another point of view when we represent ourselves reference to our actions as effects which we see before our eyes” [par. 450].
The point of view of Freedom is the one from which we consider ourselves belonging to the intellectual world. Everyone understands the distinction between the sensible world and the intellectual world through this criterion: any object whose existence is given through a modification or a passiveness of mine, is given just as a phenomenon, that is, how it appears not how it is in itself. Thus, if something appears, there must be the thing that appears: the concept of phenomenon presupposes the one of thing in itself. The difference between appearance and thing in itself correspond to “the difference between representations which are given to us from without and in which we are passive, from those which we produce entirely from ourselves and in which we show our own activity” [par. 451]. This is also the distinction, shown in the “Critics of Pure Reason”, between intellectus ectypus and intellectus archetypus; the former receives from the objects a representation and represents them just as they appear, the latter learns by creating and learning what it has created: it learns it as it is in itself.
In the Grounding the knowledge that the human being has of himself through the internal sense does not get him to know what he is in himself . “For since he does not create himself and since he acquires the concept of himself not a priori, but empirically, it is natural that he can attain knowledge even about himself only through inner sense and therefore, only through the appearance of his nature and the way in which his consciousness is affected. He must necessarily assume that beyond his own subject’s constitution as composed of nothing but appearances, there must be something else as basis, namely, his ego as constituted in itself.” [par.451].
The person finds in himself a faculty that distinguishes him from all other objects and from himself as affected by objects. This faculty is Reason, it is pure spontaneity.
Now, Determinism is law of the phenomenal world, therefore, the person, as Reason, as belonging to the intellectual world, is not affected by the laws of Determinism: he is free. This is Kant’s proof of Freedom. Is it satisfactory?
Later on, in the “Critics of Practical Reason”, Kant does not attempt to deduce synthetically Morality from Freedom, as he tried to do in the Grounding by stating that Freedom was the necessary condition for Morality, but he assumes the moral law as a “fact of the reason” from which he infers Freedom.
There have been critics blaming Kant of a sort of vicious circle, because he seemed to demonstrate Freedom by means of deduction from Morality and then to show the possibility of the Categorical Imperative deducing it from Freedom. Kant answers that there is no vicious circle because in the ontological order Freedom is the condition for Morality ( it is not possible to follow the duty for the duty if you are not free), but in the order of our knowledge, the moral law is the requirement for Freedom ( we would not consider ourselves free, if we did not think of ourselves as subject to the moral law).
Freedom is the ratio essendi of the moral law, but the moral law is the ratio cognoscendi of Freedom.
