I'm just too damn popular on this website, so let's do something about that. We're generally taught from childhood to be truthful. Lies are bad, so we're told. Let's have a look at this. To speak truthfully is to give correct information, with no regard to who is receiving this information, how powerful that person is, whether that person is just or unjust from the sender's point of view. Truth increases the power of the person in possession of it. What is the virtue of increasing the power of your enemy? Morality means acting in my self-interest, not in the interest of my enemy. If I am forced to speak to an enemy, I should lie whenever possible. The determination of who is friend and who is enemy is a separate question which should be resolved first before speaking of truth and lies. There is also a large class of people who are not now 'friend' or 'enemy'. In general it is probably better to speak truthfully to such people, assuming that they are friends, on the self-fulfilling prophesy principle, but that is subject to error.
That he may be worthy of defeat at your hands. To best your enemy on his own ground is nobler than success by deceiving him about your own.
Thanks, Dejavu. I'm not noble. I'm out to win. As football coach Knute Rockne supposedly said, "You show me a good loser, and I'll show you a loser." Having said that, it's also true that if I live a moral life, and if I'm considerate of others, I'm less likely to have enemies in the first place. Right now, I'd be hard put to think of anyone in my life who needs to be lied to. But tomorrow could change.