A reader of my blog approached me with a question regarding the difference between total depravity and total inability. Apparently, some Arminians had distinguished the two terms claiming that they believe in total depravity but not total inability.
Generally, total depravity refers to the first of the five points of Calvinism. It is the belief that humans are "totally depraved" due to the effect of original sin. This does not mean that humans are as evil as they could be (utter depravity) but that sin effects every part of human existence. Every part of humanity is deeply corrupted by sin. There is therefore no free will by which one can choose to follow God apart from grace. A depraved will can never choose that which is spiritually good.
Total inability is a more specific term. While depravity refers to the entire effect of original sin on a person, inability refers specifically to the fact that men and women are unable to make a decision to follow God, or put their faith in Jesus. It takes a divine work of monergism to convert the soul.
While I had not previously encountered Arminians making this distinction, I understand why the distinction is made. Historical Arminianism has typically confessed total depravity. According to Jacob Arminius, man's nature is so corrupted by the fall that apart from grace no one would ever make the choice to convert to the Christian faith. However, God in His grace had mercy on the human race. God decided to give prevenient grace to all men. Prevenient grace doesn't convert, but frees men's wills to the extent that they now can choose to accept or reject the gospel. This allows them to both say that apart from grace no one is converted, but also that man does have the ability, through grace, to accept or reject the gospel.
Both Lutherans and Calvinists often refer to Arminians as "semi-Pelagians" in their approach to grace and free will. However, this distinction points us to the fact that their is a great difference between Arminianism and semi-Pelagianism. Semi-Pelagians, best exemplified by John Cassian in the 5th century, argued that people can, apart from grace, make the first movement toward God. At that point grace takes over and finishes the work of salvation. (Though Cassian admitted that in certain circumstances grace did make the first movement) Thus, semi-Pelagianism rejected both total inability and total depravity.
Arminianism, rather than being semi-Pelagian, is semi-Augustinian. The finest proponent of this perspective in the early church was Gregory the Great. Being greatly influenced by Augustine's writings on grace and free will, Gregory acknowledged that apart from grace no one could believe the gospel. However, Gregory admitted that a preparatory grace was given by which men could choose to either accept or reject the gospel.
If you would like to read further on this distinction, I would recommend Roger Olson's book Arminian Theology: Myths and Realities