CORPUS CHRISTI, TX (Catholic Online) - G. K. Chesterton famously said that the Christian doctrine of original sin, a doctrine as "practical as potatoes," was the one doctrine of Christianity that could most easily be empirically proved, which I suppose also means it is the least reasonable to deny. 

A  bit of extrospection of human history and our fellow men coupled with a bit of introspection of our own souls should quickly inform us that there is something presently not quite right with us. 

Extrospection should led us to the conclusion of St. John:  "For all have sinned and fall short of the glory of God."   (Rom. 3:23)

Introspection should lead us to the same place that St. Paul found himself when he said: "For I do not that good which I will; but the evil which I hate, that I do." (Rom. 7:15). 

Though reason cannot tell us the source of this inner fracture within man, we really have no reasonable basis to deny the "indisputable dirt," as Chesterton called it, of original sin.  As long as there are persons who can feel exquisite pleasure at skinning a cat as Chesterton says (or, we might add when discussing Islam, killing black dogs), and we believe in the goodness of God and his creation, then we are compelled to believe in something like original sin to explain this situation. 

As the Catechism teaches: "Sin is present in human history; any attempt to ignore it or to give this dark reality other names would be futile," and not only futile, but false.  (CCC § 386)  In the words of St. John: "If we say that we have no sin, we deceive ourselves, and the truth is not in us."  (1 John 1:18)  This is true for both actual sins and original sin.

Based upon the revelation contained in Scripture (for without such revelation we might know of original sin's manifestations, but would be ignorant of its source, its meaning, and of its cure), the Church identifies the source of this flaw in all men.  "Revelation gives us the certainty of faith that the whole of human history is marked by the original fault freely committed by our first parents." (CCC § 390)  This first sin of our parents, in particular the effects it has had on all mankind, is the Christian doctrine of original sin.

Whether in the context of a Christian understanding Islam, or a Muslim understanding Christianity, the Christian doctrine of original sin, as taught by the Church, must be properly grasped.  It behooves us to review the doctrine as revealed in Scripture as understood by the Church.

Original sin is called "original" because the explanation for our current predicament is found at the origin of humankind as well as at our origin (i.e., at our own origin or conception). 

With respect to Adam and Eve, the sin was actual, personal to them.  With respect to us, it is called original "sin" only in an analogical sense, as "it is a sin 'contracted' and not 'committed'" by us; it is "a state," in which we had no choice, "and not an act" in which we had a choice.  (CCC § 404) 

Original sin is the result of the "Fall" of mankind, the primeval actual sin of the first human couple--Adam and Eve--that affects us all as their progeny.  It is an event historically albeit highly-figuratively-related in the third chapter of the book of Genesis.  That revelation, implicit in Genesis Chapter 3 and elsewhere (e.g., Gen. 8:21; Prov. 22:15; Ps. 14:2, 51:5, Job 14:1, 4, 15:14-16; Jer. 17:9; Eccl. 9:3), has been amplified by the teachings of St. Paul, who construed the narrative of Genesis under the light of Christ.  (Cf. Gen. 3:1-8; Rom. 5:12 ff.  See also  1 Cor. 15:21-22; Eph. 2:3)  

As the Second Vatican Council summarizes it: "What Revelation makes known to us is confirmed by our own experience. For when man looks into his own heart he finds that he is drawn towards what is wrong and sunk in many evils which cannot come from his good creator. Often refusing to acknowledge God as his source, man has also upset the relationship which should link him to his last end, and at the same time he has broken the right order that should reign within himself as well as between himself and other men and all creatures." (Gaudium et spes, 13)

The doctrine of original sin is tied to the doctrine of original justice (iusitia originalis), which is also sometimes known as original righteousness or original grace.  Original sin is tied to original justice because it is the explanatory doctrine of how we lost original justice.  Original sin is also tied to Jesus Christ through whom we regain original ...