Many conventional systems share common themes. This page is to document them.
The good touch principle says that cards touched by clues are assumed to be good. If a clue touches a card that is not good, it is called bad touch. Depending on the system and gamestate, cards duplicated in other player's hands may or may not count as good.
The strong good touch principle takes the good touch principle as an imperative: do not bad touch. If you bad touch, that fact should be demonstrated. This is the version used by H-Group conventions and many conventions based on it, via Signal Shifting
The weak good touch principle
A clue to a player is good enough if it provides them with a safe action when they did not already have one. If the team is playing with a default action convention and the clue not otherwise valuable, the player can take it as a sign that their default action was not safe; everyone will understand that their default action on future turns will be a different one.