Gaslighting is a form of psychological manipulation intended to gain control and dominance over a targeted individual.
The term comes from the 1944 film Gaslight, in which a husband tries to convince his wife that she’s insane by causing her to question herself and her reality. In the movie he dims the gas lights in the home and when his wife comments on the change in the light, he denies that it has changed at all.
Examples of gaslighting include telling a person that they are making things up, denying an external reality (such as saying it is not raining when it obviously is), telling a person they have a bad memory, repeatedly asking if the person is sure (of their perceptions, thoughts or feeling), telling someone they are too sensitive, or denying that they said or did something when there is proof to the contrary. And of course, it is about a pattern of behavior. Any one example in isolation is not definitive proof that the person is trying to gaslight.
But a repetitive pattern of these types of verbal manipulations are powerful means of control which is why it is used by cult leaders. However, most people run across this in their intimate relationships with family or partners and it is considered a form of emotional abuse. There is ample evidence of the destructive and long-lasting effects of gaslighting on an individual. And it takes effort and a healthy support system to get a person back to trusting themselves and their own perceptions and feelings. Therapy can be an incredibly important tool in helping someone deal with the aftereffects of relationships like this, which often include other forms of abuse.