What is Total Depravity?
Total Depravity, as the name suggests, is the idea that mankind as a species is totally depraved. A common misunderstanding of this doctrine is that it states man is constantly as evil as he can be, or that we are somehow incapable of doing good works. In order to refute that, one would only have to examine your standard unbeliever. These are just as capable of character development, for better or for worse, as any believer. But this is not what most Calvinists believe. Rather, they believe that every aspect of the human condition has been totally corrupted by sin. We have deceitful hearts, and so we do not seek, or desire, or even understand the things of God, and even our ability to accept the Gospel is non-existent. Thus, Calvinists generally reject the concept of free will to some degree. This is opposed to the Arminian understanding of depravity, that being Partial Depravity. Partial Depravity affirms the effect of the fall on mankind, but not to the detriment of free will. We can still seek God of our own accord.
The Bible Brain Position
Though I don't agree with Total Depravity, it's easy to see how Calvinists have reasoned it from the scriptures. The spiritual state of mankind is, indisputably, depraved. Scripture explicitly tells us that the heart is deceitful above all things, and desperately wicked, such that it cannot be understood (Jeremiah 17:9), as well as that no one is righteous, nor do we seek God (Romans 3:10-11). Statements like this make it very easy to sympathise with the Calvinist viewpoint. The question is, do these statements mean we are unable, to seek God or simply that we are unwilling to do so? I contend that the answer is the latter. As human beings, we are able to control our actions, but not necessarily our desires. For example, we can control whether or not we will eat an apple, but we cannot control whether we will like that apple. Those who do not like apples will generally not eat apples if other options are available. Continuing up the scale, consider working out. Working out is hard, and many people do not like doing it. Thus, not all of us do. This is another example of cannot vs. will not. Unless you're as unfit as me, the chances are you can do 25 press-ups right now, but I'm guessing you probably won't. Of course, you might do so just to spite me (go on, I dare you ;) ), but this is, again, a case of cannot vs. will not. I can generally do about 5 without dropping to my knees, 10 if I'm in top shape, but I will not do any right now. Because of sin, our desires are quite warped. An apple is a good thing, and I would imagine most people are quite happy to eat one of their own accord. Working out is a good thing, but probably less people will willingly work out than eat an apple. As we continue up the scale, we find things that are better for us that less people willingly do, until finally, we find something that is so incredibly good for us, yet due to our sinful nature, we just don't want to do it. With this in mind, I want to examine 1 Corinthians 10:13. 1 Corinthians 10:13 is a very popular and well known verse among Christians. It tells us "There hath no temptation taken you but such as is common to man: but God is faithful, who will not suffer you to be tempted above that ye are able; but will with the temptation also make a way to escape, that ye may be able to bear it." In other words, no matter what you think about unbelievers, it is indisputable that Christians, at the very least, are 100% capable of not sinning. Every time we are tempted, God gives us a way out of that temptation. Yet, we all know we do not always take that way out. When we, as Christians, sin, that is 100% our fault. God did not allow us to be tempted beyond our abilities, God even gave us a way out of that temptation, we chose not to take the way out, and we gave in to the temptation anyway. We are able to bear the temptation, yet we do not. Why? Well, it's because we are still depraved, even while we are in Christ. Although God is sovereign, perfectly capable of preventing us from caving to temptation, this is not His responsibility. He has given us the ability to bear the temptation. Yet we do not. It does not stretch the imagination too much to suggest that the same is true for unbelievers. We know that God does not tempt anyone to sin (James 1:13), yet clearly we still face temptation. A believer has both motive and ability to seek God's will when we are tempted, yet we still sin. An unbeliever may lack the motive, but we can reverse engineer our own state as Christians to suggest that they do not lack the ability. This is why God still gives them commands. This is why they are still punished when they disobey. They are not being forced to sin, they are sinning according to their own will. Another thing that I believe refutes total depravity are statements from God about alternative realities. An excellent example I typically point out is Jeremiah 26:3, where God says "perhaps everyone will listen and turn from his evil way...". This is not a God of ignorance. He knows both the hearts of those receiving His message, as well as how they will respond when they hear it. That means that when we later read that actually, the people did not listen and turn from their evil ways, God knew it. Yet, He said perhaps they would. There are two logical conclusions from this. Conclusion 1: God knew it was 100% impossible for them to listen, and He lied, or Conclusion 2: God knew they would not listen, but also knew they could. Given that God Himself cannot lie (Titus 1:2), I am compelled by reason to accept the latter conclusion: They could have listened to God's warnings, yet in their depravity, chose not to. A more compelling argument I like to use is the example of Sodom (with similar examples in Tyre and Sidon). In Matthew 11:23, Jesus tells Capernaum that if He had performed His works in Sodom, it would have remained to that very day (in other words, Sodom would have repented, and the disaster the Lord planned would not have come upon them). He says the same of Tyre and Sidon in Matthew 11:21 and Luke 10:13, both times stating that they would have repented in sackcloth and ashes.
This shows a shortcoming of Total Depravity. Jesus does not say "if I'd done my works there, I would have made them repent". He says "they would have repented". This tells us that repentance is a matter of the heart. Jesus is angry that Capernaum is filled with people who are too hard hearted to repent, as He wishes they would, but Sodom, Tyre and Sidon were all apparently capable of repenting if only God would show them that they should. Interestingly, there is one example in scripture of when God seems to think it is too easy to make people repent. In Mark 4:10-12, we are told the purpose of parables. Jesus tells the disciples "Unto you it is given to know the mystery of the kingdom of God: but unto them that are without, all these things are done in parables: That seeing they may see, and not perceive; and hearing they may hear, and not understand; lest at any time they should be converted, and their sins should be forgiven them." (CF. Isaiah 6:10). This, to me, suggests that if Jesus had spoken plainly His whole ministry, more people might have actually followed Him. As it was, they instead walked away from Him saying things like "this is a hard saying, who can understand it?" (John 6:60). With all this in mind, I can understand why Calvinists hold to Total Depravity, and it is indisputable that the Bible presents some doctrine of Depravity. Not even a hardcore Arminian can deny that. However, I contend that Calvinism's Total Depravity undermines man's responsibility, and, depending on the extent to which we take it, pushes the responsibility for sin in a direction it ought never go: Towards the Holy God, who will never so much as tolerate sin, much less force people to commit it.
If so be they will hearken, and turn every man
from his evil way, that I may repent me of the evil,
which I purpose to do unto them because of
the evil of their doings. - Jeremiah 26:3 KJV