Since a supernatural cause is by far the most unlikely one, you look at the possible natural causes. Unless you can eliminate all possible natural causes, there is no reason to jump to a supernatural one.
Sounds good but a little too simplistic for my taste and level of experience although I agree with the spirit (no pun intended) of your statement.
The usual phenomena are sightings, sounds and moving objects. Add to this, odours, possesion, channeling etc and the eliminination of "all possible natural causes" would require a vast amount of knowledge from such areas as the physical, biological and psychological sciences, Technology, engineering, construction, plus knowledge of local history and landscape. Add to this that it may not occur in your home, but a workplace or a place that you are visiting or staying in. Your enquiries may be highly impractical, unwelcome even career damaging. In plain language 'it is not going to happen'.
What I believe is possible is the utilization of efforts by interested people, therefore forums such as this are of use and value. Associations can be formed, data collected, stored and compared on a global basis. This I believe is the future of paranormal research.