I’ve been a Catholic, but still don’t understand what the sin of presumption is. I may be guilty of it and do not even realize it.
Perhaps the simplest sin of Presumption is believing that we can get away with sin because we presume in advance God’s forgiveness.
http://www.newadvent.org/cathen/12403a.htm
“”Presumption is here considered as a vice opposed to the theological virtue of hope. It may also be regarded as a product of pride. It may be defined as the condition of a soul which, because of a badly regulated reliance on God’s mercy and power, hopes for salvation without doing anything to deserve it, or for pardon of his sins without repenting of them.””
You should probably just presume you are guilty.
Presumption is where you "presume" in advance that you will have God's forgiveness, and use that presumption as an excuse to sin. In many cases, it is a sin that you WANT to commit, and go ahead and commit it anyway, knowing you can go to Confession later and confess it, and be forgiven. Hence, you are trying to "get away with something" - but God doesn't let us get away with legalistic tricks.
Example (perhaps a bit extreme): You (a fictional person)are a Catholic man, and all the guys in your office you want go out to a strip club together after work on a Friday evening for drinking and "carousing". You know it is wrong, and involves committing one or more sins, quite probably mortal sins, and yet you also want to hang with the guys, and it also sounds like fun to have a "guys night out". You reason in advance that even though you know it is sinful to participate, you want to go and have fun, and you further reason that you will be sorry afterwards, and will go to Confession and be given penance to do, and hence God will forgive you. You may even tell yourself that this is the only time you will do such a thing, and you won't do it again after this.
So, you go ahead and do it, and then go to confession the next day, and receive absolution from the Priest. In addition to other sins, you are probably guilty of the sin of presumption for assuming in advance you can sin at will, just as long as you ar sorry for it, and go to confession afterwards (hopefully, one of the sins you confessed was "presumption"!!).