Our imagination is different to our sense of perception. When we perceive things, we have access to only a limited amount of information. The difference between perception and imagination is that imagination calls upon what we know and uses that to create a more detailed version of reality – or a quasi reality.
The interesting thing about Sartre’s version of imagination is that he believes that the things we imagine are created from a mixture of past impressions combined with more recent knowledge. We turn imaginary objects into an idealised version of themselves, and tend to interact with them in our heads as if they were real. In our minds, the objects are real and have real properties, traits and behaviours that limit what we do with them.
Sartre believes that the ability to imagine makes us ontologically free, and stops us from being trapped in the “real” world. He believes that if you cannot imagine then you cannot enjoy freedom of thought or choice. It is that freedom of choice that makes us human and separates us from machines. The world that we live in is not a world that is constituted from the outside, but rather it is something that we have made in our head, and our intentions towards that world affect how see see it. Sartre’s entire outlook on psychology hinges around this crucial distinction and the idea that we can affect the world as we see it simply by changing what we imagine.