How can believing a lie be a grave sin when you dont know you are being lied to,and also you dont know you are being led into error.

also when we look at the three conditions for mortal sin we see.

1.grave matter must know it is wrong
3 you must have full consent

An individual who has been led into error, and does not know what they are saying is wrong. I dont think that fits the second requierment.

Why would you think believing a lie in good faith is a sin?

Believing a lie is never a sin.

Well, sometimes sin by believing a lie, like not believing in God, for instance.

Something for thought,

Since Eve believed Satan, and did eat from the tree, she believing a lie, did not sin?

I don’t recall ever hearing that believing the lie of Satan was Eve’s sin (but I could be wrong). Her sin was in disobeying God. She knew what God wanted, yet chose to disobey him. Her sin was disobedience (which also carries an element of pride int it).

Grave matter may be the matter of mortal or venial sin. Formal sin is wrong and known by the actor to be wrong, so there will be culpability when freely commited.


1790 A human being must always obey the certain judgment of his conscience. If he were deliberately to act against it, he would condemn himself. Yet it can happen that moral conscience remains in ignorance and makes erroneous judgments about acts to be performed or already committed.

1791 This ignorance can often be imputed to personal responsibility. This is the case when a man "takes little trouble to find out what is true and good, or when conscience is by degrees almost blinded through the habit of committing sin."59 In such cases, the person is culpable for the evil he commits.

essentially are most grave sins a form of erronious judgement?

DISCLAIMER: The views and opinions expressed in these forums do not necessarily reflect those of Catholic Answers. For official apologetics resources please visit