In Reformed circles, the doctrine of original sin has often been described by the phrase “total depravity.” That it’s called “total depravity” is explained in one sense because the letter “T” fits so neatly into the historic acrostic TULIP, which defines the so-called “five points of Calvinism.”
Nevertheless, the word total with respect to our depravity may seriously mislead. It could suggest that our fallen natures are as corrupt and depraved as possible. But that would be a state of utter depravity.
I prefer to use the phrase “radical corruption” perhaps because the first initial of each word suits my own name and nature, R.C., but more so because it avoids the misunderstanding that results from the phrase “total depravity.”
Radical corruption means that the fall from our original state has affected us not simply at the periphery of our existence. It is not something that merely taints an otherwise good personality; rather, it is that the corruption goes to the radix, to the root or core of our humanity, and it affects every part of our character and being.
The effect of this corruption reaches our minds, our hearts, our souls, our bodies — indeed, the whole person. This is what lies behind the word total in “total depravity.”
What is most significant about the consequences of the fall is what it has done to our ability to obey God. The issue of our moral capability after the fall is one of the most persistently debated issues within the Christian community. Virtually every branch of Christendom has articulated some doctrine of original sin because the Bible is absolutely clear that we are fallen from our created condition.
It all comes down to this, to the issue of moral ability... apart from the regenerating work of the Holy Spirit that God performs in the souls of the elect, no person in His own power is able to choose godliness, to choose Christ, or to choose the things of God. That ability to come to Christ, as our Lord Himself declared in John chapter 6, is an ability that can only be the result of the regenerating power of God the Holy Spirit.
Excerpt from "Radical Corruption"