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Hello. Kant said, imagination is a blind but indispensable function of the soul, without which we should have no knowledge whatever, but of which we're scarcely even conscious.

Imagination has been most obviously the companion of artists, scientists, leaders and visionaries, but what exactly is it and why do all of us possess it?

When did human beings first develop an imagination and why? How does it relate to creativity and what evolutionary function does creativity have?

And is it possible to know whether our brain's capacity for imagination is still evolving?

With me to discuss this is Dr. Susan Stewart, lecture in philosophy of mind at the University of Glasgow, Steven Mithin, professor of early prehistory at the University of Reading, and Sam Azaki, professor of neurobiology at the University of London and author of inner vision and exploration of art and the brain.

Susan Stewart, what do we mean by imagination in everyday life?

I think there are a number of possible definitions of what imagination might be. There are two very clear ones that Kant gives us.

The first is bringing to mind something which is not wholly present, so being able to imagine, for example, my cat lying asleep on the couch at home, a cat that is clearly not in the studio.

And the other definition, which is a much more complex definition, is putting together the sensory experiences I have, perhaps with some application of the understanding to synthesize or conjoin my thoughts to create complex thoughts, which I can then put into propositional terms.

So those are two definitions that Kant offers us, the second much more complex leading to knowledge and perhaps our beliefs.

I wanted to just stop there. The mundane we can call it, the idea of imagination, you can imagine your cat back at home asleep if the cat is asleep and so on and so forth. Everybody gets that.

Let's have another crack. Let's just try to unwrap the second one a bit more.

Could you give us an example on the way to that?

Yes. For example, I am having a flood of sensory experience now, what William James calls a bombardment of stimuli.

In that bombardment of stimuli, I am picking out certain sorts of stimuli, so I'm selecting things which are important and putting to one side things which don't really appear to be of great importance at present.

This bombardment of stimuli is really a flood of sense data, and in that flood of sense data, I apply concepts to that flood of sense data.

When you say sensory, you're seeing, you're hearing, you're smelling and so on, strictly the five senses sense data.

But this sense data is organized and unified, Kant says, by applying concepts from my understanding.

I got a bit confused between understanding and imagination there.

The understanding is a complex of concepts which allows me to order things temporally, so I can say that this is an experience which is current and there are previous experiences which I'm able to bring to mind but which are not present.

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