Many commentators have noted the difficulty of conceptualizing and measuring terrorism (Crenshaw, 1981; Schmid and Jongman, 1988; Hoffman, 2008). These difficulties can be seen on both conceptual and methodological levels. On the conceptual level, terrorism has never received a universally accepted definition that distinguishes it from other forms of political violence and crime. This was brought home to me in a recent trip to India, where a member of an audience in Uttar Pradesh, upon hearing my lecture on terrorism, complained that I had not distinguished "good terrorists" from "bad terrorists." The interlocutor was referring in particular to the Communist Party of India—Maoist, which not only engages in a fair amount of behavior that many would classify as terrorism, but at the same time participates in nonviolent legitimate political and social activities. And this is not an isolated example. Quite a number of groups that are credited with terrorist attacks—ANC, PRI, IRA, Hamas, Hezbollah, to name a few—simultaneously engage in legal nonviolent activities. Indeed, many of the most prominent terrorist groups in the world—including the Shining Path, ETA, the IRA, the LTTE, and the FARC—often conceive of themselves as freedom fighters and have a loyal constituency who may denounce terrorism but are, indeed, relying on these groups to advance their political agenda. This fundamental characteristic of terrorism no doubt explains in large part why international organizations such as the United Nations have not succeeded in adopting a universally-accepted definition (European Commission, 2008:3-4).
LaFree, Gary. 2018. "Conceptualizing and Measuring Terrorism." In Routledge Handbook of Terrorism and Counterterrorism, ed. Andrew Silke. New York: Routledge. https://books.google.com/books?id=23tqDwAAQBAJ&pg=PT2&dq=%22Routledge+Handbook+of+Terrorism+and+Counterterrorism%22+andrew+silke&hl=en&sa=X&ved=0ahUKEwi3kajPz43dAhWIt1kKHUu9AAcQ6AEIJzAA#v=onepage&q=gary%20lafree&f=false