In Kant philosophy, Freedom is defined as a concept which is involved in the moral domain, at the question: what should I do?
In summary, Kant says that the moral law is only that I know myself as a free person. Kantian freedom is closely linked to the notion of autonomy, which means law itself: thus, freedom falls obedience to a law that I created myself. It is therefore respect its commitment to compliance with oneself.
Practical Reason and Freedom
Practical reason legislates (makes laws and requirements) of free beings, or more precisely the causality of free beings. Thus, practical reason is based on freedom, it is freedom.
Phenomena, in the Kantian thought, are subject to the law of natural causality: each event is the effect of another, and so on to infinity. Unlike the phenomenon of man, in the moral rule is free, ie, it has the power to self-start condition.
Kant ethics is mainly based on the concept of free will and autonomy.