What is the Catholic concept of grace? This question reminded me of a question I've had for a long time:  What is the Catholic concept of grace?
A look at the dictionary says:

grace [greys]
noun

favor or goodwill. Synonyms: kindness, kindliness, love, benignity; condescension.
a manifestation of favor, especially by a superior: It was only through the dean's grace that I wasn't expelled from school. Synonyms: forgiveness, charity, mercifulness. Antonyms: animosity, enmity, disfavor.
mercy; clemency; pardon: He was saved by an act of grace from the governor. Synonyms: lenity, leniency, reprieve. Antonyms: harshness.


I've always felt that #3 was the most relevant in the context of Christianity, but the way I have heard Catholics and Catholic literature speak about the topic, it seems there is a more specific, and almost &quot;tangible&quot; concept of grace (and graces) at work.
The above mentioned question uses the phrases ...the same graces... and But what graces are not conferred...?
As I'm accustomed to &quot;the grace of God&quot; being a singular (or perhaps mass) noun, the concept of &quot;graces&quot; confuses me.
For most Catholic questions there are two places to start:


Summa Theologica, by Thomas Aquinas
Catechism of the Catholic Church


So for this question I will use this from the CCC (#2)
http://www.vatican.va/archive/ccc_css/archive/catechism/p3s1c3a2.htm

And from Summa Theologica this:
http://www.newadvent.org/summa/2111.htm

So there are two types of graces that come from God through Christ and the Holy Spirit, to help heal our sin, to sanctify us:


Sanctifying grace is a habitual gift, a stable and supernatural
disposition that perfects the soul itself to enable it to live with
God, to act by his love.
Habitual grace, the permanent disposition to live and act in keeping
with God's call, is distinguished from actual graces which refer to
God's interventions, whether at the beginning of conversion or in
the course of the work of sanctification.


There are two other types of graces that are given by the Holy Spirit to help us to do God's will, which are a subdividing of the habitual grace from above:


There are sacramental graces, gifts proper to the different
sacraments.
There are furthermore special graces, also called charisms after the
Greek term used by St. Paul and meaning "favor," "gratuitous gift,"
"benefit." Whatever their character - sometimes it is
extraordinary, such as the gift of miracles or of tongues - charisms
are oriented toward sanctifying grace and are intended for the
common good of the Church.


There are two types of grace, the first is a sanctifying grace which helps to unite us with God (#1 in the first group) and the second is a gratuitous grace, which allows someone to lead others to God (the second group).  This is gratuitous because, much as when Moses was told to lead, he suggested his brother (a better speaker) instead, but, because of God Moses was able to lead, to do more than he expected to do.

So, we look at the cross as an example, where there is a grace that goes between us and God (the vertical part) and the horizontal bar is where we are tied to each other, as we help each others to be with God, so the gift of God has two distinct part, and the RCC differentiates between them.

This leads to a discussion on the RCC's view on justification, but that is beyond the scope of this question, so I will end it here.