"What is a revolution" seems like an odd question at first, because events that are called revolutions take on several different forms. There is the scientific or technological revolution, which is different from the cultural revolution, and both are different from the political revolution. Revolutions can also come in different sizes as well: is a revolution that only impacts a small community less of a revolution than one that impacts the entire world? Because there is so much variation on what is considered revolutionary, it would be very difficult or even outright impossible to restrict the meaning of revolution to a single, concise definition. However, while they may be vastly different in substance, true revolutions all share two qualities: the relatively immediate change they bring (their impact), and that change's influence on the larger community (their legacy).
Whether or not a revolutionary ideal is truly revolutionary depends on its success in changing the society that it refers to (whether that is the entire world or simply a niche community). For example, the messages of nonviolent resistance, the unacceptability of injustice, and the morality of disobeying unjust laws in Dr. Martin Luther King Jr.'s "Letter from Birmingham Jail" were major themes of the Civil Rights Movement, as well as major factors to its success. The letter is directly connected to a social revolution, and is therefore directly revolutionary itself. The same cannot be said of Nicolaus Copernicus' De revolutionibus orbium coelestium. While its messages would be used by the scholars whose work would encapsulate the Copernican Revolution, and are therefore revolution-making, they cannot be revolutionary as they did not directly affect the scientific community themselves.
The letter also inspired other, similarly revolutionary actions and messages from King's peers, which is also part of the reason it is revolutionary. To be revolutionary, one must incite other revolutions (or at least reactions) either expanding upon or in reaction to the original revolution. In this sense, a truly revolutionary action is one that instigates a long process of other revolutionary action. This qualifier for revolution is fairly obvious, as it could be said that the instigation of further change is part of the direct change that revolution brings. However the distinction between direct change and influenced change is still necessary, as the revolutions inspired by a previous revolution are still revolutions in their own right. The legacy of revolutions is most noticeable in technology or culture: for example, the music created with revolutionized versions the modal system was itself analyzed and expanded upon, creating further revolutions in music theory. This qualifier may be why Lapham takes umbrage with new and upcoming technologies advertising themselves as revolutionary: while their different and more powerful systems may find widespread adoption and adaptation in the community, that direct change and influence has not yet occurred. The advertisements are predicting that technology will be revolutionary when whether it actually will remains to be seen.
Of course, when defining revolution, at least in terms of social revolution, it is necessary to at least discuss the intersection of violence in it. Is violent action – not just changing a society, but forcibly removing the previous society with that change – a requirement for revolution? Lapham certainly thinks so, as he asserts that the civil rights movement was reformative but not revolutionary. And a majority of revolutions in the past feature a violent deposition of the previous order. However, though such acts are extremely likely to happen in times of revolution – as all it takes for violence to occur is a single person willing it to happen – the revolution itself does not require violence. Revolution can be violent, but it can also be peaceful reformation. In some cases, such as the actions of the RAF, the use of violence invalidated whatever revolutionary ideals the movement may have had. This is not to say that revolutions cannot be violent, or that the impact of a revolution equals progress. Sometimes the change a revolution brings is regressive, and its 'legacy' is the attempts to undo the damage the damage it caused.
This section of my notebook contains notes on the definition of revolution within Dostoevsky's Demons, as well as the context which led to that definition. In Demons, as with my definition, social revolution is a fundamental change not just to a country's political regime but to its entire society; a political overthrow that doesn't change society or isn't caused by change in society isn't revolutionary.