What is Lying and truth?
Lying by definition is the act of not telling the truth. Truth by definition is, what is. We don't own truth. It is not ours. We may have a right to it or its origin may stem from us. (Yet our origin ultimately stems from God so we can't properly say truths originate from us for all truth is God's truth.)
When one lies, it is an act against another person. It is withholding something that is rightfully theirs. This doesn't mean you have to tell everyone ever dark dirty truth about yourself. We don't have a right to every truth out there. Generally, though, we do have a right to the truth.
So, when one lies, he/she is essentially stealing from another individual, holding back what is another's. That being so, my position on lying is that it is generally unethical to lie.
Nazis Soldier Objection
Because of a lack of space, I will deal with only one objection. It is called "The Nazis Soldier Objection." Let's say you live in Poland or Greece during the Nazi occupation and you're hiding Jews in your home. The Nazis soldiers storm your home and demand you tell them where the Jews are hiding. What do you do? Do you tell them the truth or lie?
The utilitarian in you would be shouting "lie, lie, lie." The Kantian would be saying "I wish I wasn't Kantian right now." The virtue ethicist would be saying "My system wasn't popular during this time so I don't know."
My response would be to lie. As an authority in your life, the Nazis soldier has the right to the truth. So if they asked for where is the butter then you would want to tell them the truth. But because their authority has been compromised and their right to the truth of the location of the Jews is forfeited, it is permissible to lie to them. Why? If one lacks the right to the truth then there is no obligation to give them the truth.
A Further Issue - Deception
Furthermore, it is ethical to deceive them if, as in the case of the Nazis, the opposite of deception would give them the truth, which is not their right to have. I don't have space to develop this thought anymore but that's the basic thought.
I want to qualify my above response to the Nazis Soldier Objection. Given my context as a 20th century Christian who lives in America, I find it hard to come up with situations where it is ethical for me to lie. Rather, I believe that in order to protect my consciences, it is better for me to always tell the truth, given my general situation in life doesn't change. It is only in extraordinarily conditions that lying becomes an ethical option for me.