Anger
Anger is an emotional response to a grievance; real or imagined; past, present or future. Rage refers to an extreme degree of anger associated with a loss of calmness or discipline (in the case of human conduct).
Often based in a sensation or perception of threat, anger can be considered an emotional component in the increased threat response (part of the broader "stress response") whereby the charged emotional state produces physiological effects (increased adrenaline, cortisol), thereby producing behavioural effect of heightened stress and aggression.
Anger may be "provoked" (or triggered) by perceived threats, like conflict, or by abstract concepts such as injustice.
There are many physical conditions that increase the potential for one to become angry. Common contributors to irritability include fatigue, hunger, being in pain, sexual frustration, recovery from an illness, or the use of certain drugs. Other causes are hormonal changes, such as those associated with PMS, giving birth, and menopause, physical withdrawal, and bipolar disorder. Research also shows that some individuals can be genetically predisposed to higher levels of anger.
A practical explanation of the components of anger:
The behavior that manifests and the physiological state (or sequence of physiological events that occur) when (1) An individual attributes to another person/organization/object a source of pain/deprivation (present or anticipated), and (2) Chooses behaviors (physical or cognitive) to stop or oppose it.
The key here is the choice to oppose the source of the pain. Without opposition, we would be left with fear behaviors (running away in the face of pain, for example). The pain/deprivation does not have to be a physical pain/threat, it can be emotional pain or abstract (i.e. being lied to, or political, such as the compromise of democratic values).
The source of pain can be directed at objects (i.e., the Universe, God, a low hanging branch). Because there is pain, however, does not mean anger is necessarily present (for example, bumping a nose into a glass pane, and feeling embarrassed).
The 'opposition' to pain does not have to be physically visible. The person can simply think "I want this to stop," or "I am against this." An example of an observable behavioral measure could be attempts to verbally communicate one's pain (often in a loud voice).
Humans often exhibit anger behaviors empathically. For example, reading an article about a minority experiencing racism. We are not the victim, per se.
Anger is usually magnified and extended in time when a cognitive decision is made about the intent of the individual (or organization or object) attributed to causing the pain. In other words, if we decide the pain/deprivation was intentional, "deliberate," the emotion is usually more intense.
Anger and predisposition to violence
At the end of the 19th century, Sigmund Freud, the father of psychoanalysis, argued that individuals are born with an innate aggressive instinct, and when this is blocked, they have a natural urge to become hostile or angry. A century later, this view was deprecated by the American Psychological Association and the American Anthropological Association, who in 1988 reviewed the available research and concluded that people are not genetically predisposed to violence, and that violence cannot be scientifically related to natural evolutionary processes. At the beginning of the 21st century, the consensus is reversing again, as recent research, conducted with the benefit of the fully-mapped human genome, has begun to pinpoint specific genes that increase the risk of socially harmful behavior such as aggressiveness, anti-social behavior, suicide, etc. (See this topic's discussion page for citations.)
Noticeable effects of anger include:
More acute senses. Desire to yell or to move quickly and forcefully. The eyes are open wider than usual and the pupils are dilated. The face reddens, but then may turn pale. Increased physical strength. Speech and motion are faster and more intense. Tense muscles. Bloodlust