A. Sins committed without reflection or consent are called material
sins; that is, they would be formal or real sins if we knew their
sinfulness at the time we committed them. Thus to eat flesh meat on a
day of abstinence without knowing it to be a day of abstinence or
without thinking of the prohibition, would be a material sin.

Q. 286. Do past material sins become real sins as soon as we discover
their sinfulness?
A. Past material sins do not become real sins as soon as we discover
their sinfulness, unless we again repeat them with full knowledge and
consent.

Q. 287. How can we know what sins are considered mortal?
A. We can know what sins are considered mortal from Holy Scripture; from
the teaching of the Church, and from the writings of the Fathers and
Doctors of the Church.

Q. 288. Why is it wrong to judge others guilty of sin?
A. It is wrong to judge others guilty of sin because we cannot know for
certain that their sinful act was committed with sufficient reflection
and full consent of the will.

Q. 289. What sin does he commit who without sufficient reason believes
another guilty of sin?
A. He who without sufficient reason believes another guilty of sin
commits a sin of rash judgment.

Q. 290. {57} What is venial sin?
A. Venial sin is a slight offense against the law of God in matters of
less importance, or in matters of great importance it is an offense