A medium is, in effect, much like a radio and can tune in to a world of activity that, for the most part, other humans are unable to do. Indeed, by comparison most people are only like a telephone, which really cannot be 'radio-tuned' to a station. However, though a genuine medium can tune in to both 'invisible and inaudiable stations' that others are unaware of, the 'broadcast signals', as in a radio, depend on the antenna, the 'station' broadcasting and indeed, the 'reception range of wavelengths'. Realistically though, it actually depends and lies in the medium's development level as to his or her efficiency. Accordingly, mediumship can be categorised basically as novice, intermediate, advanced or very advanced.
However, sadly, some never move on from their initial level because they think that they are developed. But no medium or anyone else can ever be fully developed or know everything about any subject! But in mediumship especially, study and practice should be - nay must be - always a continuum, in order to improve on, or move to a higher level than they are presently at. Accordingly, mediums should daily continue to hone their talent to the best possible level to demonstrate fully the truth of life are life. After all, this is a medium's primary obligation and function. There is subjective [via the mind] and objective [entities physically seen] mediumship, though [actually uncommonly] some can have both talents. [As already stated there are 'mental' and 'physical' mediums, but some do enjoy and practice both as mental and physical mediums.]
The above description, plus delineations of over 30 types of phenomena that are included under the umbrella of Mediumship, can be found in our 20 page booklet 'A Glossary of Spiritualist Terms' at $1.50 each] availbale from The Spiritualist Alliance [on Sundays] or by post [$4.00]