The moment we start mentioning concepts such as the soul we leap into a world of speculation. Pretty pictures of cats do not substitute for a serious discussion. I no longer believe in what I was taught by a fraudulent faith from a mythical book and therefore I must also reject such fanciful notions as souls, spirits and ghosts. If I were to learn that indeed there is something to consciousness beyond the brain and nervous system I would be thrilled. To get to that point would need evidence.
This is a summary of the evidence as far as I've ever read:
1 / Reincarnation stories
2 / NDEs
3 / Sightings of ghosts
4 / The subjective and intuitive experience of self
These can all be discussed elsewhere but it is clear that none of these produce evidence of a consistent or sufficient quantity to argue for anything beyond statistical chance, confirmation bias, perception mistakes, planted memories, chemical flooding of the brain and the temporary overstimulation of parts of the brain. This is not to dismiss them but to simply show that these do not meet the requirements to argue for a consistent phenomenon.
This is a summary of the evidence against a spirit IMO:
1 / It is not required under any biological definition of life. Cell division, DNA replication, respiration, procreation etc. need no additional factors to explain them.
2 / All human behaviour can be traced to biological and chemical origins and do not argue for some as yet unmeasured energy. Chemical conditions induce happiness, sadness, anger, fear and so on. A brain that is learning grows new neural connections. A brain that is damaged loses functionality. Some brains produce or experience abnormal chemical levels leading to such constructs as depression, bipolarity, genius and so on. The use of chemicals to redress these balances can remove the behaviour.
3 / When the brain returns to its natural state consciousness ceases ( we call it sleep but it has many measurable stages) We do not experience this state, no accessible memories are laid down, no perception is constructed for us with the slight exception of REM.
4 / With the exception of obvious physical trauma deaths the process of death is not specific and occurs in stages. Sometimes it takes years as parts of the brain shut down. People declared dead can be resuscitated. People may go unconscious over a long time until the automatic signalling system portion of the brain shuts down and the heart stops beating. Brain activity will continue to flicker for some time afterwards in autopilot. If a spirit were an essential part of life it would be clear when death occurred, every single time.
If we argue for a spirit we must conclude that it itself has no memory, is totally dominated and controlled by the biological systems of the body, plays no part in determining emotional state, carries no character or state at birth ( children's behaviour absolutely matches well studied brain development paths), does not maintain character ( amnesia, alzheimers and so on) , is unable to maintain a sense of self independently ( deja vu, anaesthesia, being drunk, illness or physiological stress induced delirium) , has not been observed at any level, micro or macro in any biological systems nor is it predicted by any models ( no model predicts it and no unsolved biological question would be solved by it.)
It seems the greatest argument for a spirit is based on religious ideas, the need to explain reality as having some unmeasurable, mysterious essence which privileges the conscious being and flatters them as being not only vital in a vast universe but actually the cause of it ( the world was built for us idea.)
