The only certainty in life is death. Or less melodramatically: the future is uncertain; things change. Most cultures acknowledge this as axiomatic, and when it is thought through it becomes clear that at least two worlds must exist: the knowable world, and the unknowable world. The knowable world consists of everything that can be experienced, thought, imagined: everything we could possibly talk about. The unknowable world contains everything we cannot experience or imagine – the world of feelings we will never feel, possibilities that will never materialize. Deleuze called these two sides of reality the actual and the virtual. My teacher calls them the External and the Internal. Science concerns itself with the process of externalization – with exploring the knowable world – making the unknown known. Spiritual work on the other hand concerns itself with a process of internalization – of becoming internal. We can never know the unknowable, but we can enter it and touch it by switching on the unknowable part of ourselves. This is the true nature of Mind – it is the Internal. Our usual use of mind – specifically thinking – is a gross externalization of Mind, designed to objectify the self and hence the world.