Do you exist?

My brother, Bob, asked me, “Is there anything that you are sure exists but that is not material?”

My short answer would be, “no”, but instead I replied, “I feel like everything can be put on an existance scale. On one end of the scale, say the left end, are things which I feel pretty sure exist and things on the other end, say the right end, of the scale I’m pretty sure don’t exist. This is not an absolute scale. Each thing is placed on the scale relative to other things on the scale. For example my shoes would go to the left of elves and other non-material things would go to the right of elves. So I wouldn’t say I’m sure things like ghosts, souls, angels, demons, etc. exist. I’m just less sure they exist.”

I forgot to mention to him that I think ideas exist and are not necessarily material, but can ideas exist apart from a mind? Is an idea written on paper still an idea if no one is around to read it? By the way, in my opinion the mind is a physical object made of neurons, synapses, etc.