Start with the definition, because it does real work. In social psychology, aggression is behavior intended to harm another person who is motivated to avoid that harm. Every word earns its place. Intent is required: a dentist causes pain but means none; a missed punch is aggression even though it harmed nobody. And "behavior" means aggression is an act, not a feeling — anger is an emotion you have; aggression is a thing you do. Assertiveness, competitiveness, and ambition, whatever your gym teacher said, are not aggression at all.
Bodhi says
Keep one distinction loaded for the exam and for life: hostile aggression is hot — impulsive harm driven by anger, where hurting is the goal. Instrumental aggression is cold — harm as a means to some other end (money, status, territory). A barfight is hostile; a mugging is instrumental; a hockey check to intimidate a scorer is instrumental even though it looks hot. Most of this page's machinery — frustration, heat, cues, alcohol — feeds the hostile kind.
Frustration → aggression: the old law and its smarter revision
The field's first grand theory was admirably blunt. The frustration–aggression hypothesis (Dollard, Doob, Miller, Mowrer, & Sears, 1939) declared that frustration — being blocked from a goal — always produces an urge to aggress, and all aggression traces back to frustration. It captured something real: the snapped pencil after the crashed file, the horn leaned on in gridlock. It also came with a useful corollary, displacement — when the true source of frustration is unavailable or too powerful to attack (your boss), the aggression finds a safer target (the door, the dog, the intern).
But "always" was never going to survive contact with data. People respond to frustration with despair, redoubled effort, or a shrug; plenty of aggression (the cold, instrumental kind) involves no frustration at all. The lasting fix is Berkowitz's (1989) reformulation: frustration is one member of a larger family of aversive events — pain, insults, heat, crowding, foul odors — all of which produce negative affect, and it's the negative affect that primes aggression. Two upgrades hide in there. First, anything that feels bad can push toward aggression, not just blocked goals. Second, the push is a readiness, not a reflex — whether it becomes behavior depends on the situation. Which raises the question: depends how? Berkowitz had an answer for that too.
The weapons effect: can a cue pull the trigger?
In a famous experiment, Berkowitz and LePage (1967) angered participants, then gave them the chance to shock another person. On the table nearby — supposedly left over from another study — sat either badminton racquets or a revolver and shotgun. Angered participants delivered more shocks in the presence of the guns. Berkowitz's summary became the field's best one-liner: "The finger pulls the trigger, but the trigger may also be pulling the finger." Aggressive cues in the environment, the idea goes, prime aggressive thoughts and lower the threshold for acting on an existing readiness.
Replication status — honestly mixed
The weapons effect has a genuinely contested record, and you should know it. A comprehensive meta-analytic reassessment (Benjamin, Kepes, & Bushman, 2018) found weapon cues reliably increase aggressive thoughts — that part is solid — but once publication bias is accounted for, the evidence that mere weapon presence increases aggressive behavior is much weaker and less certain than textbooks long implied. Hold it the way this course keeps teaching you to: the cognitive priming is well-established; the behavioral effect is plausible but not proven at the size the classic story claimed. See Science Corrects Itself for why "shrank under scrutiny" is the system working.
Aggression is learned: Bandura's Bobo doll
Everything so far treats aggression as something situations push out of us. Albert Bandura's point was different: much aggression is something we learn — by watching. In the landmark Bobo doll studies (Bandura, Ross, & Ross, 1961), preschoolers watched an adult either play quietly or batter an inflatable clown doll — punching it, hammering it, shouting "Sock him in the nose!" Later, mildly frustrated and left with the doll, children who had watched the aggressive model reproduced the attacks — often move for move, catchphrase for catchphrase — while children who watched the calm model rarely did.
This is social learning theory in one image: aggression can be acquired by observation and imitation, no personal frustration or reward required. Follow-ups added the accounting: children imitated more when the model was rewarded, less when punished — vicarious consequences. The Bobo studies did for aggression what the seminarian study did for helping: relocated the cause from inside the person to what the situation, and the culture, has been teaching them. It's also the launchpad for the debate below.
Situational fuel: heat, alcohol, provocation
Heat. Berkowitz's aversive-events account predicts it, and the data deliver at every scale: violent crime rises in hotter months, hotter cities, and hotter years; batters get hit by more pitches on hot afternoons. A sweeping quantitative synthesis across fields — from lab studies to civil conflicts — found higher temperatures reliably associated with more interpersonal violence and even intergroup conflict (Hsiang, Burke, & Miguel, 2013). The mundane version you already know: the argument that never would have happened in October happens in the August parking lot.
Alcohol. Alcohol is aggression's most reliable accomplice — implicated in a large share of violent crime — but the mechanism is more interesting than "alcohol makes you mean." Alcohol myopia (Steele & Josephs, 1990): intoxication narrows attention to the most salient, immediate cues and strips away the further-out considerations — consequences, norms, the other guy's perspective — that usually inhibit aggression. Drunk aggression is a failure of the brakes, not an engine of its own; a provocation that sober attention would contextualize ("he stumbled, it's crowded") gets processed as pure insult. Which is why alcohol plus provocation is so much worse than either alone.
Provocation. The strongest single trigger in the lab is no surprise: being insulted, mocked, or attacked first. Most everyday aggression is retaliatory — people aggress at those they believe aggressed at them, usually with a little extra added for interest. That escalation spiral (each side repaying "just slightly more than fair") is how trivial slights compound into feuds.
The media-violence question — the field's longest argument
Does violent media make people more aggressive? Bandura's work makes the mechanism plausible: if children imitate a live model battering Bobo, filmed models should teach too. And on one side of the debate sits a large meta-analysis of violent video game research (Anderson et al., 2010) concluding that exposure is associated with small but reliable increases in aggressive thoughts, feelings, and behavior, across cultures and designs.
On the other side, critics led by Ferguson (2015) argue the literature is inflated by publication bias, flexible outcome measures, and unstandardized aggression tasks — and that when those are corrected, effects on anything resembling real-world aggression approach zero. Longitudinal work on youth largely fails to find violent gameplay predicting later violence, and society-level trends (gaming exploded while youth violence fell) at least fail to cooperate with the alarm.
How to hold the media debate like a scientist
Both sides agree on more than the shouting suggests: short-term priming of aggressive thoughts and feelings in the lab is real; media violence is at most a small contributing factor among many; and no serious researcher claims games "cause" violence in the headline sense. The genuine dispute is whether a small lab effect survives into behavior that matters. That's an effect-size and measurement argument — exactly the kind you learned to read on the methods and replication pages. Beware anyone, on either side, who sounds certain.
Who aggresses: the gender wrinkle
The headline difference is real and large: men commit the overwhelming majority of physical violence everywhere it's been measured, and meta-analysis of real-world settings confirms men aggress more physically at every age (Archer, 2004). But the textbook-simple version — "males are the aggressive sex" — misses the finding that reshaped the field. When researchers looked at relational aggression — harming others through relationships and reputation: exclusion, rumor-spreading, the strategic silent treatment (Crick & Grotpeter, 1995) — the gender gap changed character. A comprehensive meta-analysis of childhood and adolescence found the difference in indirect aggression to be negligible: girls and boys wound socially at similar rates; the male surplus is specific to direct, especially physical, aggression (Card, Stucky, Sawalani, & Little, 2008). The accurate summary isn't "one sex aggresses more"; it's "the sexes' aggression takes different shapes — and the physical shape is the male-dominated one."
Putting it together: the General Aggression Model
You now have a drawer of separate parts — frustration, cues, learning, heat, alcohol, provocation. The General Aggression Model (GAM; Anderson & Bushman, 2002) is the field's assembly diagram. Any episode starts with inputs: the person (traits, hostile beliefs, learned scripts) and the situation (provocation, cues, discomfort). Inputs feed a present internal state — arousal, affect, and cognition, each able to inflame the others. That state feeds appraisal: a fast, automatic read of the situation ("he did that on purpose"), possibly followed by slower reappraisal if there's time and capacity to think again. The outcome — aggress or not — then rolls back into the world, usually as the next person's provocation.
The catharsis myth — the folk remedy that backfires
If aggression is pressure in a tank, then venting should drain it: punch a pillow, scream into the void, "get it out of your system." The hydraulic image goes back to Freud, and it remains one of the most confidently repeated pieces of folk psychology. It is also flatly contradicted by the evidence.
The myth
Venting anger — hitting a punching bag, smashing plates, screaming — releases aggressive pressure and leaves you calmer and less aggressive afterward.
What the research finds
Venting rehearses aggression. In the definitive experiment (Bushman, 2002), angered participants who hit a punching bag while thinking about their provocateur became angrier and subsequently more aggressive toward them than people who did nothing at all. Sitting quietly beat venting. Rumination-fueled venting keeps the angry cognition and arousal alive — practice makes permanent.
What actually helps is unglamorous: time (arousal decays if you stop feeding it), distraction and incompatible states (genuine relaxation, humor), reappraisal (rereading the provocation as unintended — which defuses the "on purpose" appraisal the GAM puts at the hinge), and, over the long run, the same observational machinery Bandura identified — running in reverse. Models who respond to provocation without aggression teach that script, too; rewarded nonaggression gets imitated just as battered Bobo dolls do.
The one thing to carry out of this topic
Aggression is not a beast in the basement that needs periodic feeding or venting — that hydraulic picture fails everywhere it's tested. It's an ordinary output of ordinary machinery: aversive states priming readiness, cues and scripts supplying the form, appraisal deciding whether it fires, and each act training the next. That's genuinely better news than the myth. Pressure in a tank can only be drained; machinery can be redesigned. Cool the room, delay the reply, question the "on purpose," skip the venting session — every link in the chain is a place to intervene, and knowing the chain is how you find them.
References
Anderson, C. A., & Bushman, B. J. (2002). Human aggression. Annual Review of Psychology, 53, 27–51. https://doi.org/10.1146/annurev.psych.53.100901.135231
Anderson, C. A., Shibuya, A., Ihori, N., Swing, E. L., Bushman, B. J., Sakamoto, A., Rothstein, H. R., & Saleem, M. (2010). Violent video game effects on aggression, empathy, and prosocial behavior in Eastern and Western countries: A meta-analytic review. Psychological Bulletin, 136(2), 151–173. https://doi.org/10.1037/a0018251
Archer, J. (2004). Sex differences in aggression in real-world settings: A meta-analytic review. Review of General Psychology, 8(4), 291–322. https://doi.org/10.1037/1089-2680.8.4.291
Bandura, A., Ross, D., & Ross, S. A. (1961). Transmission of aggression through imitation of aggressive models. Journal of Abnormal and Social Psychology, 63(3), 575–582. https://doi.org/10.1037/h0045925
Benjamin, A. J., Jr., Kepes, S., & Bushman, B. J. (2018). Effects of weapons on aggressive thoughts, angry feelings, hostile appraisals, and aggressive behavior: A meta-analytic review of the weapons effect literature. Personality and Social Psychology Review, 22(4), 347–377. https://doi.org/10.1177/1088868317725419
Berkowitz, L. (1989). Frustration-aggression hypothesis: Examination and reformulation. Psychological Bulletin, 106(1), 59–73. https://doi.org/10.1037/0033-2909.106.1.59
Berkowitz, L., & LePage, A. (1967). Weapons as aggression-eliciting stimuli. Journal of Personality and Social Psychology, 7(2, Pt. 1), 202–207. https://doi.org/10.1037/h0025008
Bushman, B. J. (2002). Does venting anger feed or extinguish the flame? Catharsis, rumination, distraction, anger, and aggressive responding. Personality and Social Psychology Bulletin, 28(6), 724–731. https://doi.org/10.1177/0146167202289002
Card, N. A., Stucky, B. D., Sawalani, G. M., & Little, T. D. (2008). Direct and indirect aggression during childhood and adolescence: A meta-analytic review of gender differences, intercorrelations, and relations to maladjustment. Child Development, 79(5), 1185–1229. https://doi.org/10.1111/j.1467-8624.2008.01184.x
Crick, N. R., & Grotpeter, J. K. (1995). Relational aggression, gender, and social-psychological adjustment. Child Development, 66(3), 710–722. https://doi.org/10.2307/1131945
Dollard, J., Doob, L. W., Miller, N. E., Mowrer, O. H., & Sears, R. R. (1939). Frustration and aggression. Yale University Press.
Ferguson, C. J. (2015). Do Angry Birds make for angry children? A meta-analysis of video game influences on children's and adolescents' aggression, mental health, prosocial behavior, and academic performance. Perspectives on Psychological Science, 10(5), 646–666. https://doi.org/10.1177/1745691615592234
Hsiang, S. M., Burke, M., & Miguel, E. (2013). Quantifying the influence of climate on human conflict. Science, 341(6151), 1235367. https://doi.org/10.1126/science.1235367
Steele, C. M., & Josephs, R. A. (1990). Alcohol myopia: Its prized and dangerous effects. American Psychologist, 45(8), 921–933. https://doi.org/10.1037/0003-066X.45.8.921