You could have tried to explain what this thing you call 'spirit' is,
Entities that can appear, speak, laugh boisterously to scare solicitors out of their consultation room, touch, generally make you aware they are about and have one or more contemplate their existence to such a point that leaves no doubt.
if supernatural,
Well, are they supernatural, hmmm?
adjective: supernatural(of a manifestation or event) attributed to some force beyond scientific understanding
yes!
or the laws of nature."a supernatural being"
flip of a coin and see when the penny drops.
how it interacts with matter,
They are matter because of visual, touch and sound projection. What state of matter? Ummmm, spirit.
why you believe it exists,
It's not a belief. It is, they are. They made it clear!
