While reading Aquinas on War for a history of medieval philosophy class, I stopped over this gem:
Secondly, a man may be deceived by what we say or do, because we do not declare our purpose or meaning to him. Now we are not always bound to do this, since even in the Sacred Doctrine many things have to be concealed, especially from unbelievers, lest they deride it, according to Matthew 7:6: “Give not that which is holy, to dogs.” Wherefore much more ought the plan of campaign to be hidden from the enemy. For this reason among other things that a soldier has to learn is the art of concealing his purpose lest it come to the enemy’s knowledge, as stated in the Book on Strategy [Stratagematum i, 1 by Frontinus. Such like concealment is what is meant by an ambush which may be lawfully employed in a just war.
I suppose the idea of an ambush is not particularly inapt in argument–one might argue for a more palatable proposition only to reveal that the argument applies to something the listener finds less palatable. So you thought I was arguing for vegetarianism but I was really arguing against abortion!
I’m not sure, however, whether this is the same thing. One the one hand, the context of the ambush would suggest as much–an ambush is no good unless you attack. On the other, hiding your view from scrutiny is the very opposite of engagement, that is, the very opposite of argument.