Intrinsic Evil

Intrinsic evil is the opposite of extrinsic evil: It is an act which is naturally (intrinsically) evil, because the act itself is absolutely contrary to reason, to nature, and to God. Intrinsic evil can never be done, for it can never be good, because good can never be good and evil at the same time. For example: A truth is true. What is true is good. A lie is an untrue or false statement made with the intent to deceive. The truth cannot be true (good) and false (evil) at the same time. A lie is never true but is always false, for it is intrisincally untrue and deceptive. Hence, a lie is an intrinsic evil.

Examples
Some examples of intrisinic evils include: Veritatis Splendor, 80 Reason attests that there are objects of the human act which are by their nature "incapable of being ordered" to God, because they radically contradict the good of the person made in his image. These are the acts which, in the Church's moral tradition, have been termed "intrinsically evil" (intrinsece malum): they are such always and per se, in other words, on account of their very object, and quite apart from the ulterior intentions of the one acting and the circumstances. Consequently, without in the least denying the influence on morality exercised by circumstances and especially by intentions, the Church teaches that "there exist acts which per se and in themselves, independently of circumstances, are always seriously wrong by reason of their object".131 The Second Vatican Council itself, in discussing the respect due to the human person, gives a number of examples of such acts: "Whatever is hostile to life itself, such as any kind of homicide, genocide, abortion, euthanasia and voluntary suicide; whatever violates the integrity of the human person, such as mutilation, physical and mental torture and attempts to coerce the spirit; whatever is offensive to human dignity, such as subhuman living conditions, arbitrary imprisonment, deportation, slavery, prostitution and trafficking in women and children; degrading conditions of work which treat labourers as mere instruments of profit, and not as free responsible persons: all these and the like are a disgrace, and so long as they infect human civilization they contaminate those who inflict them more than those who suffer injustice, and they are a negation of the honour due to the Creator".
 * Gaudium et Spes, 27 Furthermore, whatever is opposed to life itself, such as any type of murder, genocide, abortion, euthanasia or wilful self-destruction, whatever violates the integrity of the human person, such as mutilation, torments inflicted on body or mind, attempts to coerce the will itself; whatever insults human dignity, such as subhuman living conditions, arbitrary imprisonment, deportation, slavery, prostitution, the selling of women and children; as well as disgraceful working conditions, where men are treated as mere tools for profit, rather than as free and responsible persons; all these things and others of their like are infamies indeed. They poison human society, but they do more harm to those who practice them than those who suffer from the injury. Moreover, they are supreme dishonor to the Creator.