You hear a pernicious rumor about Rebecca—that she is cheating on her boyfriend. You know it to be false, but rather than confront the people spreading the false rumor and reveal the truth, you let it spread. Because, after all, Rebecca did not invite you to her party.

Jonathan carries a heavy stack of books that obscures his vision. You see that he is about to step on a sharp object. Rather than warn him, you let him step on a nail, injuring his foot and causing him to drop all of his books. But… you think it was pretty funny to see.

These are examples—albeit fictionalized—of what was once called passive aggression. Although this phrase has evolved over the years to mean hostility, social exclusion, or backhanded comments, passive aggression originally meant the deliberate withholding of behaviors to ensure that another person is harmed.

We decided to go back to the original conceptualization of passive aggression, renaming it "aggression by omission," to more precisely identify this type of aggression. We wanted to compare aggression by omission to its more commonly studied cousin, active aggression—or what we call "aggression by commission." In our research, we wanted to vary whether harm to another person was by omission or commission, while keeping everything else the same.

In two laboratory studies, a total of 416 U.S. college students delivered pictures to another person (who didn't actually exist). Participants could send either neutral pictures of architecture and landscapes or aversive pictures of gore, dead animals, and rotting meat. In some versions participants could actively send the pictures; in others they could passively decline to stop those images from being sent.

This resulted in four different versions of the task, which all participants completed. Two versions involved aggression: aversive images with active action (aggression by commission), and aversive images with passive action (aggression by omission). The remaining two versions did not involve aggression: neutral images with active action and neutral images with passive action.

In addition, to investigate whether participants commit more aggression by omission or commission against someone who had provoked them, in Study 2, participants wrote a brief essay about an emotional memory, and then received either negative feedback or positive feedback from their partner on that essay before completing the picture task.  Negative feedback served as the provocation.

We found that participants were about equally likely to commit aggression by commission and omission. Furthermore, provocation had similar effects on both kinds of aggression.

Aggression by omission was not due to a general reluctance to act. Participants were much less likely to allow an aversive picture to be sent than a neutral picture. By passively declining to stop aversive pictures from being sent, participants deliberately allowed another individual to be harmed.

Previous research on moral psychology found that harm caused by inaction is judged as less harmful and less immoral than harm caused by direct action. Therefore, we expected that our participants would judge aggression by omission as less harmful than aggression by commission—even though we kept the objective level of harm the same.  Contrary to our expectations, participants viewed their aggression by commission and aggression by omission as equally harmful. Indeed, although they viewed both kinds of aggression as equally harmful, we suspect that participants who aggressed by omission felt disconnected from the harm they caused, which could further increase aggression by omission.

In sum, our research showed that people are equally willing to passively aggress by omitting actions that could prevent harm as they are to actively aggress by committing harmful acts.  Furthermore, both types of aggression—by commission and by omission—happen more when people are provoked, and people believe that their aggression by omission is just as harmful as their aggression by commission.  These findings suggest that aggression by omission is an important type of aggression that should not be discounted or minimized as less harmful.

Although aggression by omission may be easier to excuse or hide, aggression by omission is an important type of aggressive behavior that researchers and practitioners should be careful not to overlook. Many scales that measure aggression and programs to reduce aggression focus solely on active aggression—to the detriment of their efficacy. Giving equal attention to aggression by omission can help ameliorate real-world violence.

For Further Reading

Parton, D. M., & Chester, D. S. (2023). Aggression by omission: Redefining and measuring an understudied construct. Aggressive Behavior.

Drew Parton is a Ph.D. candidate in social psychology at Virginia Commonwealth University studying the antecedents and outlets of aggression.