This is the way the Church uses the terms in various documents all over the place…even sometimes in the same paragraph such as for example:
Compendium of the Catechism:
- What is required to receive Holy Communion?
1385-1389
1415
To receive Holy Communion one must be fully incorporated into the Catholic Church and be in the state of grace, that is, not conscious of being in** mortal sin**. Anyone who is conscious of having committed** a grave sin** must first receive the sacrament of Reconciliation before going to Communion. Also important for those receiving Holy Communion are a spirit of recollection and prayer, observance of the fast prescribed by the Church, and an appropriate disposition of the body (gestures and dress) as a sign of respect for Christ.
“Hence,
in the church’s doctrine and pastoral action, grave sin is in practice identified with mortal sin.” Pope John Paul II Reconciliatio et Paenitentia 17.
In MISERICORDIA DEI it is also noted:
“Individual and integral confession and absolution are the sole ordinary means by which the faithful, conscious of
grave sin…
and in this document:
vatican.va/holy_father/john_paul_ii/speeches/1998/march/documents/hf_jp-ii_spe_19980320_cardeal-baum_en.html
“The sacrament of Penance is meant to take away personal sins committed after Baptism: first of all** mortal sins**, then venial. If the penitent has committed more than one mortal sin, they can only be remitted all at once. In fact, the remission of serious sin consists in the infusion of the sanctifying grace which has been lost, and grace is incompatible with any and every serious sin. Venial sins are to be regarded differently…”
nd in ECCLESIA DE EUCHARISTIA
“If a Christian’s conscience is burdened by
serious sin, then the path of penance through the sacrament of Reconciliation becomes necessary for full participation in the Eucharistic Sacrifice.”
Pope Benedict XVI in his Catecheses with Children said:
"Only in that case, when you are in a state of
“mortal” sin,** in other words, grave (sin)**, is it necessary to go to confession before Communion. This is my first point. "
vatican.va/holy_father/benedict_xvi/speeches/2005/october/documents/hf_ben_xvi_spe_20051015_meeting-children_en.html
and here
“The faithful, in their turn, must seek to receive and to venerate the Most Holy Sacrament with piety and devotion, eager to welcome the Lord Jesus with faith, and having recourse, whenever necessary, to the sacrament of reconciliation so as to purify the soul from
every grave sin.”
vatican.va/holy_father/benedict_xvi/homilies/2007/documents/hf_ben-xvi_hom_20070511_canonization-brazil_en.html
and an example from Moral Theology:
“
Consequently, mortal and “grave” sins are identical”. P146 Our Moral Life in Christ MTF/Scepter
and of course one can find too references to certain things being grave sins …such as purjury…on the other level the objective level…
on both levels the Church uses all three terms interchangablly