Final answer:
The 'double edge of impulse' refers to the human tendency to engage in exciting tests of courage, tempered by awareness of the potential risks.
Step-by-step explanation:
When Montague refers to the “double edge of impulse,” he is talking about the dichotomy of human instinct to both seek out excitement and test one's courage, while simultaneously recognizing the potential dangers and consequences that such impulses may bring. This concept is exemplified in various literary contexts. For instance, in Shakespeare's Romeo and Juliet, the titular characters' impulsive actions lead both to the exhilaration of forbidden love and to the tragic outcomes that result.