Gaslighting lies on a spectrum. Some gaslighters don’t know they’re gaslighting and are largely unaware of how their behavior is affecting the other person. But some gaslighters are very well aware of what they are doing, and it is done with intention and without remorse. Should the person engage in additional behaviors that fall under the spectrum of a narcissistic personality disorder, then the likelihood of them intentionally gaslighting you is much greater.
People who are dealing with gaslighting often wonder about the person’s motives. If the gaslighter doesn’t know they’re gaslighting, it gives them a sense of hope. Essentially, people on the receiving end are trying to gauge how much patience they should have with their abuser. For example: Maybe if they don’t know what they are doing, I can show them, and the conversation can be more productive.
But importantly, what would actually change if you knew what their motive was? It may help you learn to navigate the situation more skillfully (for example, if you knew that their motive was to cause doubt, then that may empower you to stand firm in your truth), but it is not necessary to know their motives in order to set boundaries.