TravisandJill, From Baltimore Catechism No. 3:
Q. 789. When is our Confession entire?
A. Our Confession is entire when we tell the number and kinds of our sins and the circumstances which change their nature.
Q. 790. What do you mean by the "kinds of sin?"
A. By the “kinds of sin,” we mean the particular division or class to which the sins belong; that is, whether they be sins of blasphemy, disobedience, anger, impurity, dishonesty, etc. We can determine the kind of sin by discovering the commandment or precept of the Church we have broken or the virtue against which we have acted.
Q. 791. What do we mean by "circumstances which change the nature of sins?"
A. By “circumstances which change the nature of sins” we mean anything that makes it another kind of sin. Thus to steal is a sin, but to steal from the Church makes our theft sacrilegious. Again, impure actions are sins, but a person must say whether they were committed alone or with others, with relatives or strangers, with persons married or single, etc., because these circumstances change them from one kind of impurity to another.
Q. 792. What should we do if we cannot remember the number of our sins?
A. If we cannot remember the number of our sins, we should tell the number as nearly as possible, and say how often we may have sinned in a day, a week, or a month, and how long the habit or practice has lasted.
Q. 793. Is our Confession worthy if, without our fault, we forget to confess a mortal sin?
A. If without our fault we forget to confess a mortal sin, our Confession is worthy, and the sin is forgiven; but it must be told in Confession if it again comes to our mind.
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