Definition
Assent is the Stoic name for the mind's act of agreeing with, or withholding agreement from, an impression. An impression is any thought, perception, or interpretation that presents itself, such as the impression that an event is a disaster or that an insult has harmed us. Assent is the choice to endorse that impression as true.
For the Stoics, assent is the precise location of human freedom. We do not control which impressions arise, but we always control whether we sign off on them. The space between an impression appearing and our agreeing to it is where reason does its work.
Why it matters
How it works
When an impression arrives, the trained Stoic does not automatically accept it. Instead they say, in effect, wait, you are just an impression and not the thing you claim to be. They then examine the impression: is it accurate, and does it describe something within our control or outside it?
If the impression passes scrutiny, the practitioner assents and acts accordingly. If it fails, they withhold assent and let it pass without granting it the power to dictate emotion or behavior. This disciplined gatekeeping, practiced repeatedly, is the engine of Stoic equanimity.