 Interventions help to give content to the arrows in the corresponding DAG. If variable \(X_i\) is a parent of \(X_j\), this means that there exists some setting for all of the other variables in the model, such that when we set those variables to those values by means of an intervention, intervening on \(X_i\) can still make a difference for the value of \(X_j\). For example, in our original model, Gas level is a parent of Flame. If we set the value of Igniter to 1 by means of an intervention, and set Gas knob, Gas connected, Meat on, and Meat cooked to any values at all, then intervening on the value of Gas level makes a difference for the value of Flame. Setting the value of Gas level to 1 would yield a value of 1 for Flame; setting Gas level to 2 yields a Flame of 2; and so on.