The article contains an analysis of a few sentences and concepts in the field of bioethics of two authors: Peter Singer and Kazimierz Szewczyk. In these statements may be noted logical errors undermining the value of the arguments of the authors. The main mistake it seems identifying the concepts with names. The authors rightly distinguish different levels of human development, but draw the dubious conclusion here that it indicates the different categories of people or persons: biological (genetic) and moral (ethical). People belonging to the first category would have different rights than those of the other. Moral status of the human, and especially being a person, it would depend on the degree of its development. Furthermore, they use the term "criteria of humanity", suggesting that the very origin from a man is not enough to be a man, which is also dubious.