The truth is, the official line on this is, until there is scientific evidence that supports their existence, spirit guides are seemingly phantasms and figments our imagination. They are something the brain creates to seemingly externalise something we cannot accept as being ourselves. Spirit guides are seen as fantasy figure. That is the scientific viewpoint, basically.
My opinion is based on the fact that in over 45 years of connecting with the Otherworlds I have never had a separate entity coming forward and announcing to me that they are a spirit guide. So for me, it is very much myself that makes the connections, gathers the information and I only have myself to blame when I get it wrong. I've pretended at times to have spirit guides to conform with the general consensus of open circles I've attended. I didn't want to appear different so I made it up as I went along. This I feel is what many others do, and it has become the new age fashion accessory to have guides. Everyone is welcome to their own perceptions and beliefs. Guides I do believe are essentially parts of ourselves most of the time.
There are rare exceptions when I believe lost loved ones, friends and other world good Samaritans do step in to give us a helping hand. But are they the cliched 'spirit guides' ... no I don't think so. The mind is a very powerful tool and it can convince us that something internal is actually something separate to us ...
