Sobre o problema da mentira na filosofia prática de Kant

The research examines the problem lie in the thought of Immanuel Kant. This field of law, of the history of political morality, we seek to investigate the Kantian rejection of falsehood and unconditional obligation to be truthful. Defends the thesis of the exception to lie and not be objectionable in two cases, namely: the torture and before the murderer. Thus, it is demonstrated that it is possible the exception to lie under the law, politics and history, considering the perspective of harmony of external freedoms and the idea of moral progress. In this sense, it is argued that the source of law is established to guarantee the external freedoms. From the point of view of morality, reaffirmed the absoluteness is that for Kant the duty of veracity, but it points to the possibility of a practical rule that allows the lie based on human dignity, weighting values as political equality, respect for rational agents, as well as the principle of humanity which teaches always treat the other as an end in itself.