An efficacious desire, i.e. one that includes the deliberate intention to realize or gratify the desire, has the same malice, mortal or venial, as the action which it has in view. An inefficacious desire is one that carries a condition, in such a way that the will is prepared to perform the action in case the condition were verified. When the condition is such as to eliminate all sinfulness from the action, the desire involves no sin: e.g. I would gladly eat meat on Friday, if I had a dispensation; and in general this is the case whenever the action is forbidden by positive law only. When the action is contrary to natural law and yet is permissible in given circumstances or in a particular state of life, the desire, if it include those circumstances or that state as conditions, is not in itself sinful: e.g. I would kill so-and-so if I had to do it in self-defence. Usually, however, such desires are dangerous and therefore to be repressed. If, on the other hand, the condition does not remove the sinfulness of the action, the desire is also sinful. This is clearly the case where the action is intrinsically and absolutely evil, e.g. blasphemy: one cannot without committing sin, have the desire — I would blaspheme God if it were not wrong; the condition is an impossible one and therefore does not affect the desire itself. The pleasure taken in a sinful thought (delectatio, gaudium) is, generally speaking, a sin of the same kind and gravity as the action which is thought of. Much, however, depends on the motive for which one thinks of sinful actions. The pleasure, e.g. which one may experience in studying the nature of murder or any other crime, in getting clear ideas on the subject, tracing its causes, determining the guilt etc., is not a sin; on the contrary, it is often both necessary and useful. The case is different of course where the pleasure means gratification in the sinful object or action itself. And it is evidently a sin when one boasts of his evil deeds, the more so because of the scandal that is given.
