The initiation of force is the start, or beginning, of the use of physical and/or legal coercion, violence, or restraint. This is to be distinguished from retaliatory force and violence. It can be understood as the difference between two or more individuals getting into a fist-fight: whoever "threw the first punch" is the initiator of force, or aggressor, while the person attacked—the victim—is using non-initiatory or retaliatory force if they fight back. Moral opposition to initiation of force is complementary with the non-aggression principle which supports force only in self-defense.
There are two main types of force-initiation: direct physical and legal. The initiation of legal force is the use of government or legal proceedings to indirectly coerce a non-aggressor. Direct physical force includes all kinds of physical violence and coercion; most ethical theorists extend it to include economic features, however, they disagree on what constitutes force in this respect. Progressives and left-liberals believe that exploitation and alienation constitute the use of force, while classical liberals (and libertarians) and most Western conservatives (capitalists) insist that only officially recognized acts of fraud, theft, trespassing, and vandalism are. Theocratic and moralistic religious extremists may believe it is possible for humans to initiate force against God(s) by sinning, and that it is thus mandated that other humans act on behalf of God(s) by using retaliatory force against the transgressor. To an impartial observer, the 'sinner' would be seen as being a non-aggressor that was physically attacked, and the 'punishers' would be the force-initiators.
Many theorists extend the definition to also cover all acts of deception, lying, misrepresentation, and verbal threats, but not all agree that this is indeed initiation of force in every case, or at all, as none of these things, in and of themselves, actually cause physical harm to a person. However, the near-automatic emotional reactions can lead to severe psychological harm, hence many in the general population perceive certain verbal insults and taunts as initiatory blows which warrant immediate physical retaliation. Threats by large and historically violent entities (The State) are also an initiation of force. The highly subjective and arbitrary basis of what can constitute such responses as justifiable, along with the fact that again, no actual physical contact occurs, leaves most ethicists to concur that it is still only the person who throws the first punch who is in fact the force-initiator and that it is ultimately under the control of the target of such insults and taunts as to whether or not they are actually harmed; at any rate, it is their responsibility to control their physical reactions that directly (physically) affect others.