Q. 275.  In how many ways may actual sin be committed?  A. Actual sin may be committed in two ways:  namely, by wilfully doing things forbidden, or by wilfully neglecting things commanded.

Q. 276.  What is our sin called when we neglect things commanded?  A. When we neglect things commanded our sin is called a sin of omission.  Such sins as wilfully neglecting to hear Mass on Sundays, or neglecting to go to Confession at least once a year, are sins of omission.

Q. 277. {51} Is original sin the only kind of sin?  A. Original sin is not the only kind of sin; there is another kind of sin, which we commit ourselves, called actual sin.

Q. 278. {52} What is actual sin?  A. Actual sin is any wilful thought, word, deed, or omission contrary to the law of God.

Q. 279. {53} How many kinds of actual sin are there? 
A. There are two kinds of actual sin—­mortal and venial.

Q. 280. {54} What is mortal sin? 
A. Mortal sin is a grievous offense against the law of God.

Q. 281. {55} Why is this sin called mortal?  A. This sin is called mortal because it deprives us of spiritual life, which is sanctifying grace, and brings everlasting death and damnation on the soul.

Q. 282. {56} How many things are necessary to make a sin mortal?  A. To make a sin mortal, three things are necessary:  a grievous matter, sufficient reflection, and full consent of the will.

Q. 283.  What do we mean by “grievous matter” with regard to sin?  A. By “grievous matter” with regard to sin we mean that the thought, word or deed by which mortal sin is committed must be either very bad in itself or severely prohibited, and therefore sufficient to make a mortal sin if we deliberately yield to it.

Q. 284.  What does “sufficient reflection and full consent of the will” mean?  A.  “Sufficient reflection” means that we must know the thought, word or deed to be sinful at the time we are guilty of it; and “full consent of the will” means that we must fully and wilfully yield to it.

Q. 285.  What are sins committed without reflection or consent called?  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.