**1859 **Mortal sin requires full knowledge and complete consent. It presupposes knowledge of the sinful character of the act, of its opposition to God’s law. It also implies a consent sufficiently deliberate to be a personal choice. Feigned ignorance and hardness of heart do not diminish, but rather increase, the voluntary character of a sin.
There is more to that definition than meets the eye
If one attempts to play games with individual terms in the first part of the definition to diminish even the possibility of committing a mortal sin, that’s why the ending is added to the definition.
“Feigned ignorance and hardness of heart do not diminish, but rather increase, the voluntary character of a sin.”
IOW faux, fake, pretend ignorance, actually increases the voluntary character of a sin. IOW when one puts effort into crafting their excuse, rather than own up to their deed, they actually increase the voluntary choice they made to commit the sin in the first place.