Lawyers know that it is improper to use any means to win in the struggle that is litigation. Lay people may also understand that, at least intuitively.
Given that even war is to be conducted within limits we should be glad that this is so. The laws of war are being continuously developed through treaties and, hopefully, through development of the customary laws of war. Customary laws are binding on all nations and states, regardless of express agreement by treaty, say.
Treaties are important elements in the process of the development of customary laws.
Perfidy is the use of treacherous means against an opponent. In modern times it is cited in Article 37 of the 1977 Protocol 1 of the 1949 Geneva Conventions.
“Art 37. Prohibition of Perfidy
1. It is prohibited to kill, injure or capture an adversary by resort to perfidy. Acts inviting the confidence of an adversary to lead him to believe that he is entitled to, or is obliged to accord, protection under the rules of international law applicable in armed conflict, with intent to betray that confidence, shall constitute perfidy. The following acts are examples of perfidy:
(a) the feigning of an intent to negotiate under a flag of truce or of a surrender;
(b) the feigning of an incapacitation by wounds or sickness;
(c) the feigning of civilian, non-combatant status; and
(d) the feigning of protected status by the use of signs, emblems or uniforms of the United Nations or of neutral or other States not Parties to the conflict.”
These are wonderful words. The first two sentences are the important words; the last sentence contains examples that do not limit the definition. For instance, an escaping prisoner of war, disguised as a civilian, is not perfidious unless he/she breaches the rule in the first sentence.