A revolutionary is a person who either participates in, or advocates a revolution. The term revolutionary can also be used as an adjective, to refer to something that has a major, sudden impact on society or on some aspect of human endeavor.
The term—both as a noun and adjective—is usually applied to the field of politics, but is also occasionally used in the context of science, invention or art. In politics, a revolutionary is someone who supports abrupt, rapid, and drastic change, usually replacing the status quo, while a reformist is someone who supports more gradual and incremental change, often working within the system. In that sense, revolutionaries may be considered radical, while reformists are moderate by comparison. Moments which seem revolutionary on the surface may end up reinforcing established institutions. Likewise, evidently small changes may lead to revolutionary consequences in the long term. Thus the clarity of the distinction between revolution and reform is more conceptual than empirical.
A conservative is someone who generally opposes such changes. A reactionary is someone who wants things to go back to the way they were before the change has happened (and when this return to the past would represent a major change in and of itself, reactionaries can simultaneously be revolutionaries). A revolution is also not the same as a coup d'etat: while a coup usually involves a small group of conspirators violently seizing control of government, a revolution implies mass participation and popular legitimacy. Again, the distinction is often clearer conceptually than empirically.
According to sociologist James Chowning Davies, political revolutionaries may be classified in two ways:
According to the goals of the revolution they propose. Usually, these goals are part of a certain ideology. In theory, each ideology could generate its own brand of revolutionaries. In practice, most political revolutionaries have been anarchists, communists, socialists, Islamists, syndicalists, or nationalists.