Adam and Eve were created by God to be in full fellowship with Him. He placed them in the Garden of Eden with the power of contrary choice and with instructions to not eat from the tree of the knowledge of good and evil. Adam’s disobedience in this prohibition is the original sin. Adam was tempted by Satan to doubt the divine goodness and was further coerced to have an inward desire for God’s wisdom. Thus, original sin is best defined as Adam’s breach of covenant with God by violating God’s command, thus moving Adam from a state of holiness to unholiness and separated from fellowship with God. Consequently, because of Adam’s federal headship all humanity is under the curse of universal sin, receiving imputed guilt and inherent pollution.
The Westminster Larger Catechism confesses the fall of all mankind in this original sin (WLC Q:22) and Scripture confirms the fall through federal headship, “…in Adam all die” (I Cor 15:22) and “… just as sin came into the world through one man” (Rom 5:12). Adam and Christ are the only two persons in history that have held this office as federal head. Paul calls Christ “the last Adam” in I Cor 15:45-49 and Paul also writes in Colossians that “Christ is the head of the body, the church”, thus replacing Adam as federal head. To further understand this federal headship one must remember that humanity is considered in Scripture as a corporate entity much like bricks in a wall. Humans are so tightly connected we are better considered a wall then individual bricks. There is a natural dimension for this corporate entity to be connected. Hebrews 7:9-10 considers offspring to be “in the loins” of their ancestor. Thus as a corporate entity we were “in the loins” of Adam when he sinned. Augustine said, “by birth we are heirs of Adam’s sin.” This unity of the corporate entity is exposed when the actions of the head are considered the actions of the body (humanity). Keep in mind we are only affected by Adam’s original sin, as this was a breach of covenant, not a transgression of law. Transgressions (actual sins) are not inherited by offspring, only breaches of covenant are, in this case Adam’s original sin.
One can conclude original sin is reality when its effects of imputed guilt and inherent pollution are experienced in special and general revelation. Paul traces imputed guilt (universal sin) in his letter to the Ephesians, “…(we) were by nature children of wrath, like the rest of mankind” (Eph 2:1-3). Adam’s original sin is the reason humanity is served the judicial verdict of guilt and the judicial sentence of a sin nature, death and a cosmic curse (WLC Q:25; WCF 6:2-6). Humanity’s inherent pollution (also referred to as total depravity) is the punishment for the imputed guilt. Augustine viewed inherent pollution as punishment, as well as Bavinck who said, “Because all are considered sinners in Adam, they are all also born of him in a sinful state. Original pollution is a punishment for original guilt.” Scriptures view of fallen man can be summarized in three ways: 1) total depravity (Gen 6:5-6; 8:21; I Kings 8:46); 2) total inability to reverse the curse (Matt 7:8; John 3:3,5); and 3) real guilt, “a contradiction of God’s perfection”.  There is an absence of the image in humanity now and Paul records his struggle with this in Romans 7:7-25. Paul also records the effects of original sin in chapter 5: v.12 describes the move from sin to death to universal death to universal sin; v.13-14 describes the problem; v.15 confirms that through one man’s trespass many died; v.18 through one trespass all men are condemned. The good news Paul concludes, “so by the one man’s (Jesus) obedience the many will be made righteous” (v.19). Glory to God! It is much easier to understand original sin when the work of Christ is also in the conversation. The gospel confirms the reality of original sin as it is the freedom for humanity from original sin.
 John Murray. Collected Writings of John Murray Volume 2, 69.
 Bavinck, Reformed Dogmatics Volume 3, 94 footnote 45: Augustine, City of God, XIII, 3.
 Westminster Larger Catechism Question 25; Westminster Confession of Faith 6:2-6.
 Bavinck, Reformed Dogmatics Volume 3, 106.
 Robert Reymond. A New Systematic Theology of the Christian Faith, 450-456.