In the first part of this study, with a marked theoretical character, it is analyzed the condition of man called to live together with his neighbors. The quality of common life is offered by people’s fidelity given to truth, which, thus, becomes the foundation of communion between people. Further on, it is noticed the danger which threatens truth avowal in the social life, the gravest situation being the neighbor’s discrediting and, trough this, jeopardizing the common life. Understanding and avowing truth must cont of biblical exigencies concerning truth. This exigencies refer both to itself truth and to the importance of its avowing, to person’s and community good. Than it is analyzed what is not and what is lie and this is denounced like a grave form of destroying a culture which has to promote an authentic human pro-existence. The second part of the study, more practical, has in view the delicate situation in which the man can be forced at deceiving by necessity. There are not forgotten the conditions in which social-political mechanism practices an oppression of truth, and, trough this, a systematic destruction of man and of society. It is mentioned the importance of truth in publicity and in propaganda actual forms, emphasizing the good and the bad they could do. Finally, there are shown the special situations in which the professional secret and the persons who detain it must be protected.